Altiris NS 7.5 disconnects frequently

We have recently performed an in-place upgrade of Altiris 7.5 from initial 7.1. The NS got disconnected last week. It again got disconnected this week. On diagnosis we found that the Symantec Management Agent service on NS is in disabled startup mode. We haven't changed any service on the NS.

IS this is bug with SMP 7.5?