Originally Posted by
Full Bleed
What ended up working:
Deleting FG Folder (from Program Files (x86))
Using Regedit to remove the Fantasy Grounds settings from the Registry (Computer>HKEY_CURRENT_USER>SOFTWARE>Fantasy Grounds)
Reinstalling from the WebInstaller.
They had to re-open the shared modules and re-setup stuff like hotkeys, but at least it started working for them again.
NOTE: The same results may have been achieved via deleting the C:/Program Data/Fantasy Grounds folder (or maybe even just the cache from there)... but we'd spent enough time messing with it at that point so nuking the Registry Entry from orbit and, essentially, getting a fresh install up ended up being the path of least resistance. Also note that the Program Data folder is Hidden should you wish to go looking for it.
DISCLAIMER: Please recognize that if messing with your Registry or deleting any hidden folders tears a hole in the fabric of your reality, we are not responsible. This is just what worked for us. ;)