It could be a lot of things, I would do the following:
> To start of, verify if any events are coming on the AIP-SSM itself (via GUI or console)
> Is the 'Events Connection' showing as connected on the IME summary window?
> Goto Events >> Historical >> Last x duration and see if any events came from the AIP-SSM
> Double click the AIP-SSM (or right click and update the status) to get the latest certiifcate
> Restart the IME service
Regards
Farrukh