Hi all,
Here's a followup on my previous post. When I udated from 5.1.2 to 5.5 I used the 5.1.2. configuration diskette to boot, after which my system was updated to 5.5 and the Webmail error occurred. I just decide to do a clean 5.5 install, do the initial configuration manually (these basic settings remain unchanged from previous versions). Then I restored the fresh desktop backup (made with the 5.5 upgrae instalation) and rebooted. Et voila, webmail is back in business. On the reboot after restoring the backup, I noticed that "conversion from imp to turba" is now disabled.
I'm still not sure what has happened, but at least I got my system running again.
To me, it look as if the upgrade path still needs some tinkering to become as foolproof as the rest of the system.
Thanks,
Mark