TLS/SSL Negotion Failed

I am getting this message in the event viewer and have never seen it before. “Code 4149-Connection from NBRMR1001.ac.com failed %2 TLS/SSL negotiation. connection dropped.”
These are occurring about every 10-15 minutes. This is coming from the IMCas an SMTP Interface Event. Running Exchange 5.5 SP3 on NT4.0SP5.