When this occurs, verify whether the file '/tmp/AppleTalk.Muxid' is present. If the file is missing, this would explain why MAE is no longer able to access the AppleTalk stack. This file is necessary for MAE to bring up and down the AppleTalk stack cleanly. If the file is removed while MAE is running, it will leave MAE in an odd state that can only be corrected by restarting of the workstation, which will bring the AppleTalk stack back into a clean state.
Some reasons why the file may be missing are; a cron job that deletes files in the /tmp directory at night, or a user indiscriminately removes items in /tmp.