Tony is right the first thing to check is the permissions of the archive that the item resides in.
I have also seen this error when an update to the NAB was not replicated to the NAB on the EVDG.
Gather a dtrace of the directory service, nserver, and storageonlineopns.
The process will check the NAB on the EVDG, and then it will compare with the EVDirectory.
If everything is in order it should not give you that warning.