Well, the error means what it says - no notification devices were found for the user in quesiton (or all the users in question I guess) - this wont make their accounts stop working other than notificaitons wont be going out if that's expected. It does, however, indicate your system is potentially in a very bad way. The error coming back is being issued from the SQL Server - dbWalker is doing a very generic query for all notificaiton devices for a user and SQL is coming back and saying there's corruption of some kind and nothing is returned.
That's bad. You need to make sure you have a backup in place sooner rather than later.
Lots of reasons for corruption are possible, hard to say what but it could be a hard drive sector bit the dust is could be a drive going south in a hurry - no way to know but corruption is never a good thing.
If you're users don't have notification devices configured for dialout (i.e. delivering a note to a page on new urgent messages or calling them at home etc...) then they probably wont notice anything wrong. I'm curious what shows up in the SA when you open one of these users and try and access their notificaiton devices - I'm guessing some sort of error or empty page comes up.
Either way - dbWalker can't fix that kind of corruption - hence the indication that to get the user back into shape will require a delete/recreate. But as noted, please be sure to get a backup of your system in place if you haven't already.
