Sounds like a damaged record that for some reason doesn't show in database verification. Think you are going to have to work with technical support or a certified consultant to fix. If you know which client, you can try looking at the slips and see if there's one that seems to be a problem. Then you might be able to delete or purge that slip.

I agree with Caren and will echo much of what she suggests. The error is telling you it has to do with slips, but data verification isn't helping. You have some options to troubleshoot. -- You could put the same filters on the Time and Expense Slip List and open each unbilled slip for that client to see if any damage if visible and possibly fix if there, or simply delete and replace the slip. -- If that doesn't work, you could also use a Slip Selection filter on the bill and choose one of the client's slips at a time. If a specific slip results in the error you could delete and replace the slip. Good luck!

In addition to the great advice provided by Caren and SRF, please look for and delete the network locking files in your system after getting all users out of the software.