If your build works just peachy on your own PC but bombs out on your TeamCity server with the error “Default parameter specifiers are not permitted”, head over to your build step and update the Tools Version to 4.0

This way your CI build will be targetting C# 4, the version that introduced optional parameters. And yes, I realise that the correct solution here is to not have optional parameters in your codebase; the codebase is new to me and I haven’t refactored them all out yet!