Unable to send message - but no message to send

[RogerE]

Whenever I start Thunderbird recently, after a few minutes, I get an "unable to send message" popup.

However there is no message to send. I have checked the Outbox folder, and it is empty as are the drafts folders.

I am running 60.5.1 (32-bit) using Win10.

Thanks

Roger

[DanRaisch]

Have you compacted both the Drafts and the Outbox folders?
Does the same thing occur if you launch the application in Mozilla Safe Mode? http://kb.mozillazine.org/Safe_mode

[RogerE]

I'll give it a try later when I'm back home

[RogerE]

Tried both compacting (which I had already tried) and starting in Safe Mode - no popup.

This morning started up as normal. and no popup yet!