Check the UDS editor and see if you have any custom signatures created. If so, remove them, you can export them if you need to use them in the future, double check your policy(s) that the signatures are no longer part of the rule set. Then push them out to the sensors. Essentially what I believe is happening, the sensors send a signature reference number that the manager does not have in it's database. Both the signature set on the sensors and the manager must match exactly.
I am seeing this problem on my Central Manager even after upgrading to the ,22 release. Engineering is working on a fix for me so hopefully this will be fixed. We noticed that it only seems to appear under the Summary view and not if you go directly to the RTA. Support said they refresh the RTA more frequently than the Summary view and they felt this could be the reason.
It also seems to me that it is performance related. We have alot of events going into the NSM and the ICC.
When i have issue like this..normally I logout and relogin again..
It's work for me not sure yours..
I believe (poor coding in java applets) after something the reference to alert mess up etc so instead showing alert name it's shwoing it's number value