Hello, I do not know if the following can help. So just in case. I met the same problem recently on a xfce4 setup. Digging in the bug reports I found this one that matches the same error messages I had. I finally solved my problem noticing that it happened after modifying the XDG_DATA_DIRS variable and after some some paths in that variable were deleted on my system. Removing the non-existing paths from XDG_DATA_DIRS variable solved my problem. Therefore, it might be worth verifying if all paths in the XDG_DATA_DIRS actually exit (or can be accessed).
Best regards Pascal
