Can you give a bit more to go on, please. Is this something new that just started to happen to your installation, or has it always done this?
Also, you may consider installing the latest GA software maintenance release, which I think is V9.5 SP4 and see if that clears anything up.
One other thing; On the host machine, go to Start > Solarwinds(?) > Advanced Features > Services (I think, I'll have to clear this up later today, sorry). And check to see if the Alerting Service and/or Trap Service is running or stopped.