I have a user with Lots 6.5.5. When they open up the welcome page they receive an error." You are not authorized to preform that operation". This user is a roaming user as well, I havent been able to find any Access Control issues but am open to anything to figure out why the welcome page has went bonkers.
The welcome page uses the location document to get the mail file, have you checked to make sure this hasn’t changed, if someone elses mailfile is in there then they might not have access to it.
Otherwise you could try removing bookmarks.nsf and let Notes create a new one.