Update! I finally figured out what was going on. I tried to replicate the error with some sample code, but unfortunately, the code worked. But in tinkering around with the program, I figured out the problem.

I had the main.pl file, a gui.pm file and a core.pm file. The core.pm contained the logic, the gui.pm contained the Tk, and the main program had almost nothing in it. I had use Tk; in main.pl, because I started the MainLoop there, but apparently I needed use Tk::BrowseEntry; as well. I'm not sure why, but that solved my problem. My packaging command looked something like this:

I am running into other problems now, but I'll do some more research, and if I can't find anything, I'll just make another thread. This thread has been solved.