Designer.cs files and source control
svn
Solution
I recommend that you add them to your source control. They're auto-generated by the IDE, not by the build process, so should you introduce Continuous Integration (A Good Thing), then the builds will fail (as it is for you now on a clean checkout).
Artifacts that are generated via the build process (binaries, object files, "manually implemented" auto-generated source files, etc) should be excluded.
Problem
I have a web application with designer.cs files. Since they're autogenerated, I don't want to add them to source control (or do I?). However, the project file looks for them, and a fresh pull from SVN errors until you delete the references to designer.cs and then convert to web application, which is a major pain. Should I just add them to source control? Can I remove the references from the project file?