Excel 2007 Macro error

I have a spreadsheet with macros that I use for work which works flawlessly on Win XP, but when you try to run the macros on a Vista/7 machine it gives this error:

"Compile error: Can't find project or library"

It seems to be hanging up at "Trim" on this line:

NewSheet = Trim(InputBox(Mesg, Title))

Our tech support seems lost, any help?

Thanks!