>I have a projecthook class subclassed from the _base class library. The _base class library is in my project. Anytime I try to build an exe I get the error that "..._base is in use and cannot be recompiled". This error rings a bell from a long time ago. I can't seem to find the solution to this.

You have kind of answered your own question. You can not compile a file into an App/Exe if it is still in use. When the project is open, the projecthook object is instanciated. Since you have an instance of the projecthook which is based on the _base classlib AND this same _base classlib is in the current project you get the error.

I would create a copy of the _base classlib files and name them something else. Then base your projecthook class on the copied classlib.