More error message funnery

Following on from my last posting ( courtesy of Mr James S ), here's another one

I've seen this three or four times when I try and send an email.

This has started appearing since I got  PCSync working with Notes 8.5 - not sure if that's a coincidence or not. I've run NCOMPACT and NFIXUP on my mail file, and we'll see if it recurs.