I tried GrannyGeek's suggestion and seamonkey 2.03 loaded fine. I then followed her suggstion to import bookmarks and that too worked fine. I then tried to get my email (I use seamonkey for email) and it asked me to go through some sort of email set up wizard. So I renamed ~/.mozilla/seamonkey to mozilla/seamonkey2-23 and renamed seamonkey_old to seamonkey. And that worked fine, including email.
Glad it worked. I've not had profile problems for a while, but I do remember a few years ago having similar problems when updating Seamonkey.

GrannyGeek's suggestion was a lot simpler than mine. I guess I shouldn't try to suggest things at the end of a 13 hour shift....
Only thing I can think of that might explain the earlier error is that my email file is huge. Took about 10 minutes for 4pane to copy it to an external harddrive (thought I better try that before trying GrannyGeek's suggestion, she being a female and all that. (just kidding).

I think you are treading on dangerous ground there....
I have noticed that some things do get slow. For instance, I have Seamonkey set to compact folders when doing so will save 100kb or more. I've now got around 270 messages in my inbox, and when Seamonkey compacts that folder, it does make things slow down a fair bit. Some of the other folders (the Seamonkey mailing list folder for instance) are
much bigger, and that can bring Seamonkey to a crawl if I happen to try and do something while it is compacting that folder. So I guess there may be a problem if any one of your email folders gets too large.
Have you thought about breaking the email up - I used to save it to dated folders, so that I could find things by time at one stage. These days, I just use lots and lots of different folders...
toothandnail, thanks for the backup suggestions. I backup my complete home directory to an external harddrive every Sunday night, using Grsync Backup tool (root) from the menu. I do no other backup.
Getting a bit OT, but one question about your backup - what filesystem do you use on your external harddrive?
Paul.