I find myself wondering if this is related to a directory refresh issue I see regularly.
Namely that if I go to a driver (external or otherwise) and create a new directory/folder, OpenToonz does not immediately recognize that it has been created.
Therefore I can't access any files inside that folder.
Your case does appear to be different but I include my thoughts for the broader issue of file access .
In your case you are receiving a specific error message so that help with finding the fix and/or a suitable workaround.
I doubt that such a hack would work but you could try to place a copy of the glut32.dll in the root of your USB or in the directory with your files just to see if... on the very odd chance... that might resolve the issue.
I don't really think this will help but it wouldn't take long to test.
One of the reasons I include my file locating problem is that I was going to try to see if I could set up a similar situation where I could replicate what you are experiencing but can't because OpenToonz won't recognize the USB I just inserted and formatted for that purpose. The workaround in my case is to restart OpenToonz at which time that drive and directory is recognized. At present I don't see any way to refresh the directory listing manually.
Added: I should add that once I restart OpenToonz and the directory and files can be located I can load from the USB stick.