Sometimes on larger projects, or rather solutions made up of multiple projects it's a hazard that you might get your references in a twist. if you do VS will get it's knickers in a twist and put something like the following in the task list:
Warning: The dependency '[some.namespace Version=1.0.2959.19180, Culture=neutral' in project 'some project' cannot be copied to the run directory because it would overwrite the reference 'some.namespace', Version=1.0.2824.17691, Culture=neutral'.
One of the symptoms that will bring this to your attention, is IntelliSense for objects and their methods in a referenced class library project will stop functioning. Gah!
The golden rule I have found is when adding references between the projects in the solution, particularly if project A and Project B *BOTH* require a reference to project C. Make sure you add it from the Add a reference's Project tab, rather than browsing to the dll file. This way VS will see the circular dependency and sort it out, and IntelliSense will be restored, thank goodness, time for a cup of tea.