I'm trying to stop lead conversion if someone tries to convert a lead that isn't owned by themselves.
I have a custom button for leads that looks like this (Detail Page Button):

../apex/ConvertThisLead?Id={!Lead.Id}

...And the apex page looks like this:

<apex:page standardController="lead" 
   action="{!DoConvert}" 
   extensions="leadConvertController">
</apex:page>

 ...And the controller class looks like this:

public class leadConvertController {
        Public lead lObj;
        Public Id leadId;
        
        public leadConvertController (ApexPages.StandardController stdController)  {
            leadId = ApexPages.currentPage().getParameters().get('id');                    
            }
     
     
      public PageReference DoConvert()  {      
            Database.LeadConvert lc = new database.LeadConvert();
            LeadStatus convertStatus = [Select Id, MasterLabel from LeadStatus where IsConverted=true limit 1];            
            
            lObj = [SELECT ID, OwnerId from lead where id =: leadid];         
            lc.setLeadId(leadId);                       
            lc.setConvertedStatus(convertStatus.MasterLabel);                                   
            
            if(lObj.OwnerId == UserInfo.getUserId() ){  // perform the lead convert
                Database.LeadConvertResult lcr = Database.convertLead(lc);
                System.assert(lcr.isSuccess());
                Id oppId = lcr.getOpportunityId();
                String sServerName = ApexPages.currentPage().getHeaders().get('Host');
                sServerName = 'https://' + sServerName + '/';
                PageReference Page = new PageReference(sServerName+oppId);
                Page.setRedirect(true);
                return Page;
                }
            else {  // can't do the convert
                lObj.addError('You must be the Lead Owner to Convert this lead!');
                lObj.addError('Please login as the lead owner');
                }
            return null;
           }           
    }

 Everything seems fine - I get an Opportunity ID back, but the redirect never takes place.

I tried just putting the ID of the created opportunity on the URL line

(like; https://cs4.salesforce.com/006P0000004E...,) and SF replied with "Data Not Available".

Anyone know what I'm doing wrong?

Thanks,

KC