Would you like to check in all files which are checked out to you in project <project>?

This message has the following cause and solution:

• You are closing the development environment leaving files checked out.

When you close your development environment, VSS reminds you that you have files checked out of the project and prompts you to check them back in. You do not have to check them back in, but leaving them checked out may prevent other users from checking them out.