Sudden FileNotFoundException message

I am modifying an existing application in VB .NET开发者_开发知识库.

In one routine, I have added a reference to a class in a newly-referenced class library project that is part of my solution, and now I get run-time FileNotFoundException messages when the program attempts to access this routine while debugging. The error tells me that the class can't be found, what's up with that?

To be clear: if I remove the lines of code relating to the new class, I no longer receive the exception messages. If I add them back in, here they come again!

1. I have referenced the class library in the project containing this routine.
2. The class library is building properly (other projects reference same library, and use it more extensively), and the project is referencing the class library's .dll file in my "debug" folder.
3. I get no errors from other routines that use this new class (thus far).
4. I get no errors in the Error List of the IDE.

What in the world could be happening here? SH

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This is a project reference, not a reference to an assembly (DLL), right?

Are the .NET frameworks the same?

Does the project you are referencing depend on some external assemblies not included in the other project, that might be called, producing the file not found?