We had a ticket from a Zeus user unable to get a file off our DPM, while her Zeus colleagues could. I spend a long time checking the pool accounts, which were all fine, and checking the Zeus VOMS setup, which was also fine.
Finally, I looked in the logs for the grid-mapfile, where the culprit lay:
"Can't locate Term/ReadKey.pm in @INC..."
On two of the servers, disk034 and disk036, the perl-TermReadKey RPM was missing and it looks like the grid-mapfiles had not been rebuilt for a very long time - from the backups it looks like it was October when they were remade!
OK, nagios check: age of grid-mapfile and lcgdm-mapfile!