I've been having a number of issues recently and have had occasion to repair disk permissions a number of times. Hasn't sorted out any of the problems I was wanting (!) but it also meant I had to reset preferences in Mail.
No great sweat you might think except when I close the Mail Preferences window I get the message "Writing your preferences to disk has failed. The permissions on ~/Library/Preferences may be wrong or your disk may be full"
Permissions aren't wrong (I've checked and checked) and the disk is only 1/3 full

Would anyone have any ideas?
Thanks in advance!