I've created a VF page that I'm overriding the view button (detail page) for opportunities.  The related list for Opportunity Field History is causing a problem.  I've read several posts on this issue, but can't seem to get the problem resolved.

Here is the error message I'm receiving:

Validation Errors While Saving Record(s)
There were custom validation error(s) encountered while saving the affected record(s). The first validation error encountered was "Changed Field: bad value for restricted picklist field: Travel_Expenses_are__c". 

 Here is my VF page:

<apex:page standardController="Opportunity">
<apex:form >
 <apex:sectionHeader title="Opportunity" subtitle="{!opportunity.name}"/>
 <apex:pageBlock title="Opportunity Detail">
 
 <apex:pageBlockButtons location="both">
 <apex:commandButton action="{!edit}" value="Edit" />
 <apex:commandButton action="{!delete}" value="Delete" />
 </apex:pageBlockButtons>
 
 <apex:pageBlockSection title="Opportunity Information" columns="2">
 <apex:outputField title="Opportunity Owner" value="{!opportunity.OwnerId}"/>
 <apex:outputField title="Amount" value="{!opportunity.Amount}"/>
 <apex:outputField title="Account Name" value="{!opportunity.AccountId}"/>
 <apex:outputField title="Approved Min Amount" value="{!opportunity.Approved_Minimum_Amount__c}"/>
 <apex:outputField title="Opportunity Name" value="{!opportunity.Name}"/>
 <apex:outputText title="Budget and Price Me" value="{!opportunity.Price_Me__c}" escape="false" style="float:right;margin-right:135px;" />
 <apex:outputField title="Length of Agreement (Months)" value="{!opportunity.Length_of_Agreement__c}"/>
 <apex:outputField title="Close Date" value="{!opportunity.CloseDate}"/>
 <apex:outputField title="Pricing Approved" value="{!opportunity.Pricing_Approved__c}"/>
 <apex:outputField title="Stage" value="{!opportunity.StageName}"/>
 <apex:outputField title="Pricing Status" value="{!opportunity.Pricing_Status__c}"/>
 <apex:outputField title="Division VP Approval" value="{!opportunity.Division_VP_Approval__c}"/>
 <apex:outputField title="Current Contract Fee Amount" value="{!opportunity.Current_Contract_Fee_Amount__c}"/>
 <apex:outputField title="Probability (%)" value="{!opportunity.Probability}"/>
 <apex:outputField title="Debrief Link" value="{!opportunity.Debrief_Link__c}"/>
 <apex:outputLabel value="" />
 <apex:outputField title="Exclude from Pricing Report?" value="{!opportunity.Exclude_from_Pricing_Report__c}"/>
 </apex:pageBlockSection>
 
 <apex:pageBlockSection title="Contract and Account Information" columns="2">
 <apex:outputField title="Account Net Patient Revenue" value="{!opportunity.Account_Net_Patient_Revenue__c}"/>
 <apex:outputField title="Termination without Cause" value="{!opportunity.Termination_without_Cause__c}"/>
 <apex:outputField title="# Years as Client" value="{!opportunity.Years_as_Client__c}"/>
 <apex:outputField title="Termination without Cause Description" value="{!opportunity.Termination_without_Cause_Description__c}"/>
 <apex:outputField title="Client Since" value="{!opportunity.Client_Since__c}"/>
 <apex:outputField title="Hosp Req'd to Terminate GPO Relationship" value="{!opportunity.Hosp_Reqd_to_Terminate_GPO_Relationship__c}"/>
 <apex:outputField title="Existing Contract" value="{!opportunity.Existing_Contract__c}"/>
 <apex:outputField title="Non-Standard Termination Options" value="{!opportunity.Non_Standard_Termination_Options__c}"/>
 <apex:outputField title="New Contract" value="{!opportunity.New_Contract__c}"/>
 <apex:outputText value="" />
 <apex:outputField title="Auto-Renewal?" value="{!opportunity.Auto_Renewal__c}"/>
 <apex:outputField title="Contract Type" value="{!opportunity.Contract_Type__c}"/>
 <apex:outputField title="Current Agreement Length (months)" value="{!opportunity.Current_Agreement_Length__c}"/>
 <apex:outputField title="Auto-Renewal Periods (months)" value="{!opportunity.Auto_Renewal_Periods__c}"/>
 <apex:outputField title="Contract Expiration Date" value="{!opportunity.Contract_Expiration_Date__c}"/>
 <apex:outputField title="Auto-Renewal Notice Period (days)" value="{!opportunity.Auto_Renewal_Notice_Period__c}"/>
 <apex:outputField title="Current Agreement Initial Annual Fee" value="{!opportunity.Current_Agreement_Initial_Annual_Fee__c}"/>
 <apex:outputField title="Auto-Renew Frequency" value="{!opportunity.Auto_Renew_Frequency__c}"/>
 <apex:outputField title="Current Agreement Fee Structure Type" value="{!opportunity.Current_Agreement_Fee_Structure_Type__c}"/>
 <apex:outputText value="" />
 <apex:outputField title="Current Agreement Fixed Fee %" value="{!opportunity.Current_Agreement_Fixed_Fee__c}"/>
 </apex:pageBlockSection>
 
 <apex:pageBlockSection title="Expected Start Date" columns="2">
 <apex:outputField title="Expected Start Date" value="{!opportunity.Clients_Expected_Start_Date__c}"/>
 </apex:pageBlockSection>
 
 <apex:pageBlockSection title="Proposed New Agreement" columns="1">
 <apex:outputField title="High Risk Factors" value="{!opportunity.High_Risk_Factors__c}"/>
 <apex:outputField title="General Strategy / Tactics" value="{!opportunity.Strategy_Tactics__c}"/>
 <apex:outputField title="Proposed Contract Structure Description" value="{!opportunity.Proposed_Contract_Structure_Description__c}"/>
 <apex:outputField title="Opportunity Notes" value="{!opportunity.Opportunity_Notes__c}"/>
 <apex:outputField title="Previous Barriers/Issues" value="{!opportunity.Previous_Barriers_Issues__c}"/>
 <apex:outputField title="Contract Term Reductions" value="{!opportunity.Contract_Term_Reductions__c}"/>
 </apex:pageBlockSection>
 
 <apex:pageBlockSection title="Proposed Service" columns="1">
 <apex:outputField title="Department" value="{!opportunity.Department__c}"/>
 <apex:outputField title="Service Line" value="{!opportunity.Service_Line__c}"/>
 <apex:outputField title="Project" value="{!opportunity.Project__c}"/>
 </apex:pageBlockSection>
 
 <apex:pageBlockSection title="Closed Lost" columns="2">
 <apex:outputField title="Awarded to" value="{!opportunity.Competitor__c}"/>
 <apex:outputField title="Primary Reason Lost" value="{!opportunity.Closed_Lost_Reason__c}"/>
 <apex:outputText value="" />
 <apex:outputField title="Primary Reason Lost Comments" value="{!opportunity.Primary_Reason_Lost_Comments__c}"/>
 </apex:pageBlockSection>
 
 <apex:pageBlockSection title="Useful Links" columns="2" collapsible="false">
 <apex:outputLink value="https://na3.salesforce.com/servlet/servlet.FileDownload?file=01550000000BCxP" target="_blank" style="float:right;margin-right:250px;" >QHR Client Contact Worksheet</apex:outputLink>
 <apex:outputLink value="http://search.hoovers.com/cgi-bin/hol_search?which=company" target="_blank" style="float:right;margin-right:250px;" >Financial Profile</apex:outputLink>
 </apex:pageBlockSection>
 
 <apex:pageBlockSection title="Additional Information" columns="2">
 <apex:outputField title="Zone" value="{!opportunity.ZoneID__c}"/>
 <apex:outputField title="Opportunity Record Type" value="{!opportunity.RecordTypeId}"/>
 <apex:outputField title="Acct_Div_VP_Email_Address" value="{!opportunity.Acct_Div_VP_Email_Address__c}"/>
 <apex:outputField title="QHR Client On Oppt Created Date" value="{!opportunity.QHR_Client_On_Oppt_Created_Date__c}"/>
 <apex:outputText value="" />
 <apex:outputField title="zz-PricingStatus" value="{!opportunity.zz_PricingStatus__c}"/>
 </apex:pageBlockSection>
 
 <apex:pageBlockSection title="System Information" columns="2">
 <apex:outputField title="Created By" value="{!opportunity.CreatedById}"/>
 <apex:outputField title="Last Modified By" value="{!opportunity.LastModifiedById}"/>
 <apex:outputText value="" />
 <apex:outputField title="Default Start Date" value="{!opportunity.DefaultStartDate__c}"/>
 <apex:outputText value="" />
 <apex:outputField title="Opportunity Record Type Name Static" value="{!opportunity.Opportunity_Record_Type_Name_Static__c}"/>
 </apex:pageBlockSection>
 </apex:pageBlock>
</apex:form>

 <apex:relatedList list="Pricing__r"/>
 <apex:relatedList list="OpenActivities"/>
 <apex:relatedList list="ActivityHistories"/>
 <apex:relatedList list="OpportunityContactRoles"/>
 <apex:relatedList list="OpportunityTeamMembers"/>
 <apex:relatedList list="R00N50000001tDC2EAM"/>
 <apex:relatedList list="NotesAndAttachments"/>
 <apex:relatedList list="OpportunityHistories"/>
 <apex:relatedList list="R00N50000001u8uNEAQ"/>
 <apex:relatedList list="Opportunities__r"/>
 
 <apex:pageBlock title="Opportunity Field History">
 <apex:pageBlockTable value="{!Opportunity.Histories}" var="h">
      <apex:column headerValue="Date" value="{!h.createddate}"/>
      <apex:column headerValue="User" value="{!h.CreatedById}"/>
      <apex:column headerValue="Connection" value="{!h.OldValue}"/>
      <apex:column headerValue="Action" value="{!h.Field}"/>
</apex:pageBlockTable>
</apex:pageBlock> 
 
 <apex:relatedList list="Legal_Tasks__r"/>
 <apex:relatedList list="Proposal_Management__r"/>
 <apex:relatedList list="Revenue_Projections__r"/>

</apex:page>

 If I removed the Opportunity Field History related list section, the page works fine and I do not get the error message.  So, the issue is with the Field History related list.

<apex:pageBlock title="Opportunity Field History">
 <apex:pageBlockTable value="{!Opportunity.Histories}" var="h">
      <apex:column headerValue="Date" value="{!h.createddate}"/>
      <apex:column headerValue="User" value="{!h.CreatedById}"/>
      <apex:column headerValue="Connection" value="{!h.OldValue}"/>
      <apex:column headerValue="Action" value="{!h.Field}"/>
</apex:pageBlockTable>
</apex:pageBlock>

 How do I fix this error?

Thanks for any help.