Problem: COPY FAILED no write permission or out of disk space

Hello There,

I hope someone has an answer to this, it's driving me nuts!

Debian Sarge, Courier IMAP, Postfix

Getting the message "COPY FAILED no write permission or out of disk
space" about every 2 - 3 seconds... I'm not actually moving anything and
there's plenty of disk space!

I've checked the permission settings and every thing looks fine (using a
single UID and GID for all mail server related stuff.

There is no information in any logs and there doesn't seem to be anyway
to turn up the standard debugging level, well except for login
information :(

Any help/pointers gratefully received!

Thanks,

Haga