I have the following Case Button URL to create a New Case populating some of the necessary fields:

https://CS1.salesforce.com/500/e?&RecordType=012300000000TKiAAM&cas3_lkid={!Contact.Id}&cas4_lkid={Account.Id}&cas11={!Case.Origin}&00N30000000bx3i={!Case.Call_Back__c}&cas5={!Case.Type}&00N30000000c3N0={!Case.Problem_Type__c}&cas7={!Case.Status}&cas8={!Case.Priority}&CF00N30000001ZHdO_lkid={!Case.Site_AccountId__c}&00N30000000vUNK={!Case.Product_Family__c}&00N30000000bx13={!Case.Version__c}&00N30000001XRbJ={!Case.Subproduct__c}&cas14={!Case.Subject}&cas15={!Case.Description}

That is giving me the following error:
Unable to Access Page - The value of the "id" parameter contains a character that is not allowed or the value exceeds the maximum allowed length.  Remove the character from the parameter value or reduce the value length and resubmit. If the error still persists, report it to our Customer Support team. Provide the URL of the page you were requesting as well as any other related information.

If I remove the Account.Id and Contact.Id fields, the URL opens the new case but the Site_Account__c is blank so all lookups are not working properly.  The Site_AccountId__c is a second lookup to the Account object.

I have also tried this and many other field name variations with no luck:

https://CS1.salesforce.com/500/e?&RecordType=012300000000TKiAAM&cas3_lkid={!Contact.Id}&cas3={!Case.Contact}&cas4_lkid={Account.Id}&cas4={!Case.Account}&cas11={!Case.Origin}&00N30000000bx3i={!Case.Call_Back__c}&cas5={!Case.Type}&00N30000000c3N0={!Case.Problem_Type__c}&cas7={!Case.Status}&cas8={!Case.Priority}&CF00N30000001ZHdO_lkid={!Case.Site_AccountId__c}&CF00N30000001ZHdO={!Case.Site_Account__c}&00N30000000vUNK={!Case.Product_Family__c}&00N30000000bx13={!Case.Version__c}&00N30000001XRbJ={!Case.Subproduct__c}&cas14={!Case.Subject}&cas15={!Case.Description}

Any help is greatly appreciated!