I agree with Vernon Telecom, delete the mailbox and recreate it. It that doesn't not work, pull the storage medium and have a Windows PC run scandisk/repair on it as well as defrag.
Yes this problem has been around for years dating back to the first SVMi4s. Nearly impossible to track down because it is so intermittent. When you watch it via the port activity it will most like be fine.
It is not just that the message does not light the message waiting light. The message is just not there, and then 'poof' it appears the next day or worse, a few days later. The timestamp is correct. It just wasn't there before.
