The combination of a Team System solution, including a BizTalk project and an Unit Test C# project is not a good one, as I learned recently. ;-)
The problem occured, when I wanted to add a BizTalk map in an orchestration - simply nothing happened. The only thing was an bunch of errors while closing Visual Studio afterwards:
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Microsoft Visual Studio
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Unexpected error encountered. It is recommended that you restart the application as soon as possible.
Error: HRESULT: 0x80131527
File: vsee\internal\inc\vscomptr.inl
Line number: 473
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OK
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Another error was the following one:
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Microsoft Visual Studio
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Error
COM object that has been separated from its underlying RCW cannot be used.
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OK
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After unloading the Unit Test project everything worked fine again.