I think I've found the problem and fixed it. I didn't realize there was a separate forum for this mod until this morning. In that forum there is this thread...
https://vbulletin.org/forum/showthread.php?t=325733
...which describes the error and the solution, which is to disable the "Crowns in postbit" plugin. I did so and it appears that the error no longer displays (I've only checked one thread, but I think that was the fix).