Can't find Project or Library Error

I have a program which was developed in Excel 2003. It has always worked fine on my web book using Excel 2007. All of a sudden, whenever I try to enter data anywhere in the file I get an error screen which says "Can't find Project or Library". I tried replacing the file thinking it night be corrupt, but I keep getting the same error message. I clicked on the help screen but I'm not sufficiently experienced with computers to even understand what help is talking about. Anyone have any suggestions?

When you are in security, you should be able to allow vba projects, see if that helps you out.

Does the project use Calendar Controls?