Great advice! I went through this process, and it turned out to be the 124thATC plugin. Once I unloaded it from the plugins folder, it fired up right away. I was having crashing problems when loading the flight - all the time, every location and airport (custom scenery or not). Looks like it's back to normal now.
Too bad because up until now 124th was the best offline ATC plugin. It's not perfect, and none of them are, but it worked for what I needed it to do - and WAY better than default ATC. Looks like I'll have to drop the $$$ and give Pilot2ATC a try.
Thanks for the advice,
Mike