If you have enough ports and TTRs in the system - then the message lights should be turning on/off in a timely manner. I would double-check that voicemail day/time is in sync with system date/time. You may want to make sure - if the problem is sporadic that all TTRs are functioning. I would test them to be sure. If one or more are bad - when the voicemail port tries to use them - the mail light on/off will fail.
If all above is OK - and you can access the MLM via the RS232 port or modem - I would log in and shut the system down and run the port and hard drive tests. If the port tests pass - but the hard drive shows sector errors - then you may have a failing drive - which can foul all kinds of things up.
Tom Daugirdas,
President
STCG, Inc.
stcg.com