OK, here's what I've figured out so far (about what's causing the error on my end, not how to fix it, although I haven't had any problems from the error):
When I start UO with UOAssist, I get about 23 of the error messages cascading from the middle of the screen. If I open UO though the client itself, there are no issues, nor are there any when opening an additional client with EUO. Again, I haven't had any problems from the error messages, as I just close them and continue on (although I don't know if closing them is even necessary).