When trying to build a BizTalk project I got this error. Here is the solution:
1) Checking out a single XSD file does not result in the corresponding CS file being created
2) Excluding the XSD file from the project then re-including it does result in the CS file being created
3) Checking out just the BTPROJ file and the XSD file (expecting this perhaps to be similar to the exclude / re-include) does not result in the corresponding CS file being created
As detailed above, checking out every file in the solution prior to build addresses the problem.