Can't log in after attempting to download MoP

Hey all, I'm kind of at my wit's end here, so any help would be much appreciated.

I've played on Icecrown with no issues for a long time now. I wanted to try out MoP, so I installed the Mac installer here: http://forum.warmane.com/showthread.php?t=320450

I didn't change anything to any of my WOTLK files. I didn't overwrite any of my WOTLK files. I genuinely do not understand why or how installing MoP could have affected WOTLK, but it certainly did. I am unable to log in to Icecrown or Frostwolf. I can launch both game clients with no issue, but after entering my username and password, I recieve a "the information you have entered is not valid" error, eventually followed by a "Cannot log in to World of Warcraft at this time. Please try again later." error after a few attempts. I am obviously entering the same information that I have since I started playing. I tried disabling 2FA, as well.

I have tried clearing my cache, re-installing the data files for MoP, and changing the realmlist file (for WOTLK) and the config file (for MoP) to have just "set realmlist logon.warmane.com" and nothing else. I am getting nowhere.

I'm wondering if the issue is related to language packs? The MoP client came with enGB, while I usually use enUS. I tried matching the two clients to no avail. I really don't know, but now I feel like an ***** because I can't log in to either servers. I am running OS X El Capitan 10.11.16.