Hi All,
I spent a good amount of time [and a good amount of Cunning's time as well, (thanks boss!)] trying to figure out why I couldn't get MQ2 to work. I finally figured it out last night, so I wanted to post something for anyone else that might find this error in the future.
If you're using EQBC/MQ2 and getting a "command is not valid" message within the client, make sure that you aren't loading the game by launching the THF Downloader, and make sure that you've followed step 3 on the Getting Started link here:
viewtopic.php?f=7&t=1763
Once you know that step is complete, launch both EQBC and MQ2, then run the shortcut or modified executable to launch the EQ client, and everything should load perfectly.
Hopefully that saves someone some research time in the future.