cannot create /tmp/SophosBusy.lock

[W.G.J Kuiters]

I run the latest debian unstable packaged version of mailscanner
(3.27.1-1) with Sophos. From time to time I get this message (probably
when the Sophos update script is triggered):

"Cannot create /tmp/SophosBusy.lock Permission denied at
/usr/share/mailscanner/logger.pl 64"

I checked the permissions on /tmp and they seem alright to me.

What could be the cause of this?

Willem