It's probably because you never compiled your code to check for errors before splitting. You should also have Option Explicit at the top of every module and compile frequently as you code, and finally before splitting. I understand what the message means but have no idea what's causing it. When applicable, always post the error number, message, and in the case of code, what line causes it. My guess it fails in one of your modulename.procedurename calls or the procedure has gone out of scope after splitting, but without even knowing which line, that is indeed a wild guess.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.