CS0433: The type {0} exists in both Temporary ASP.NET Files dlls

I ran into this bug today and found a really simple solution that worked for me. Hopefully it can help others.

Bug:
CS0433: The type 'ASCX' exists in both '..Temporary ASP.NET Files\{0}.dll' and '..Temporary ASP.NET Files\{1}.dll'

Solution:
In your Visual Studio solution. Clean the entire solution. Then rebuild the entire solution.