Parsing error in Client Backup report. Says check log. Which log?

2 weeks ago  upgraded to NBU 7.7.1 from 7.6.0.4.   Everything went well, except now we get an error message when running the Client Backups report from the Administration console.    The message reads  "An error has occurred while parsing the report data. Please check the logs"     But I am unclear as to which logs I should be checking.     That said, it appears that a couple of the policies I've had for a long time are somehow involved.   I can run a client report if I specify a client outside certain policies, but if I specify a client in a few policies, then the error shows up.    I check the"All Log Entries" report and the "Problems" report and neither are helpful.   Everything else seems fine.

Thank you.