Symptom
You receive the following error message when you try to compile one BizTalk Server 2006 project that contains map files:
Error: Build failed. Compiler for file type '*.btm' failed. Unable to load wrapper:C:\Program Files\Microsoft BizTalk Server 2006\Developer Tools\Mapper Extensions\Microsoft.BizTalk.Security.SSPI.dll.
Resolution
The BizTalk Server 2006 compiler load this assembly from the GAC, therefore to fix this problem you must delete the Microsoft.BizTalk.Sercurity.SSPI.dll assembly from the %biztalk_install%\Developer Tools\Mapper Extensions folder.