Problem with ambiguous classes in my project

I have several CustomControls that I have written for my project. However,
when I try to compile I recieve the following warning & errors:

Warning 32 Could not resolve this reference. Could not locate the assembly
"nathansokalski_com_test, Version=1.0.0.0, Culture=neutral,
processorArchitecture=MSIL". Check to make sure the assembly exists on disk.
If this reference is required by your code, you may get compilation errors.
nathansokalski_com_test

I receive the following error for all of my classes/CustomControls:

Error 33 'Menu' is ambiguous in the namespace 'nathansokalski_com_test'.

All of my classes/CustomControls are in the same Project, and are therefore
are in the same assembly. Why is this happening? Is there some way to find
out what the other class each of these is ambiguous with is?
--
Nathan Sokalski
njsokalski@hotmail.com
http://www.nathansokalski.com/