DBML Not Backwards Compatible

If you are planning on upgrading to Visual Studio 2008 SP1 and you are using LINQ, make sure your entire team upgrades to SP1 at the same time.

While DBML is forward-compatible from 2008 to 2008 SP1, they are not backwards-compatible, meaning if you make a change to a DBML file in a project, that project will not build in 2008.

The compile will fail with this error:

Build failed due to validation errors in [path]\[file].dbml. Open the file and resolve the issues in the Error List, then try rebuilding the project.

When you look at the output, it will tell you that O/R Validation failed with an unknown error.