In case anyone else goes googling this error, I ran into it today, too. This afternoon, everything worked perfectly. Tonight, error 4101. Same FM, same QB, same record, same script, same everything. Except ... in the script I was running, I made a couple edits from a Mac that, of course, can't see all the PCQB functions because it's a PC only plug-in. I didn't touch any lines that referenced the FM Books Connector plug-in, just wrapped a few lines in an If/End If.
I solved the problem by going back into the same script from a PC and editing the script step that triggers the 4101 error (PCQB_RqNew-EstimateAdd) and saved it and voila ... no more 4101. I'm guessing my problem was due to editing from the Mac.
Gordon Shewach