"Error saving preferences" when not trying to save preferences...

[Don Green]

Any ideas what I can do to stop getting this message anytime I have DrRacket running in 2 terminals in different workspaces on linux/Ubuntu.

"Error saving preferences" is the title in the popup window.

Text in the window is:

"The preferences file is locked (because ...) so your preference change could not be saved."

I am not trying to change preferences!

The popup appears when I go back and forth between running instances of DrRacket.