Sometimes a user can experience buffer problems when they have too many profiles or authorizations. It is a good idea to periodically check to see if any users have more than 300 authorizations so that you can evaluate whether they really need that many.
SE16 > enter table USR04
Highlight the column header "Number of profiles or authorizations" and sort descending with the appropriate icon so that the largest numbers are at the top. You will see those users that have more than 300 profiles or authorizations.