Developing a BizTalk application with several orchestrations. All of a sudden an orchestration which has not been edited does not compile because some of its types are undefined.
Checking many things to no avail. Lastly shelved all changes to Team Foundation Server. Fetched the last working version from Team Foundation Server, compiled it without errors. Unshelved the previous version which did not compile, compiled it - and now it compiled!
Not sure what happened - but problem was solved.
BizTalk Server 2010. Visual Studio 2010 Ultimate.