Everyone is correct…try everything…(in order of a little to a lot of time wasted)
- Do you have bad code? Fix that first.
- Clean Solution & Restart Visual Studio
- Remove / Add References
- Check your build order w/ larger projects and verify
- Manually rebuild sub-projects
- Manually copy dlls between projects into associated bin folders
- Go get some coffee, play some pinball and come back tomorrow…you may think of something else in the meanwhile.