This error is caused by a missing schema version property in the source project.

The most likely cause of this error is that you have attempted to load a help file builder version 1.7.0.0 or earlier project file that is not valid. Check the file to be sure that it is a help file builder project file. If you are unable to solve the problem based on the reported error, open a work item in the Sandcastle Help File Builder project at CodePlex containing the details from the error message. Attach the affected source project as an example.

Other Resources