The 2.2 release notes on upgrading with auth enabled (see http://docs.mongodb.org/manual/release-notes/2.2/#synopsis) state that "you must upgrade the drivers before upgrading the mongod instance or instances", without further information on what determines if a driver upgrade is necessary.

An upgrade is necessary if the current driver version always calls getLastError on the admin database, and this information is in the driver notes. The docs could be upgraded to recommend checking the driver notes to see if a driver upgrade is necessary.