Today, after more than two weeks of vacation I run into a totally new error when trying to compile any BizTalk project. The error message was:
Build failed. Compiler for file type '*.xsd' failed. Value cannot be null. Parameter name: pUnk
Huh!??! Punk!??! What the F*** does that mean!??!
I googled on the message and didn't find much so I guess it's not a very common problem. But I found this old article KB 884412.
I'm still not sure what caused the problem but I did a repair on the BizTalk installation and the problem was gone. Hmm Maybe BizTalk had a christmas vacation too :)