I have a case open for another customer with this issue, which is currently being looked at by the developers. The "...DLL is not a McAfee trusted DLL" message is apparently caused because the agent can't load its DLLs, but I haven't been able to reproduce the behaviour.
Just to confirm - uninstalling and reinstalling the agent has no effect, is that correct? And neither does reverting to version 4?
Finally - I know you hear this a lot from support folks, but bear with me - it's unlikely that two agents would spontaneously fail in the same, highly-uncommon way, within a few hours of each other. Can you think of anything on these machines that could have changed? Were any patches installed, or new software, or new hardware? Any changes to group policies?
Right. Re-installing the agent fixed neither problem; that being the empty McTray "About..." and the reporting problems.
I'm going to attach an Excel spreadsheet which shows something interesting concerning patches. I'll explain. SERVER1, which is no longer reporting in and has the McTray problem, had eleven patches installed the very day that it stopped reporting in. Those patches, listed by their KB number are listed under the SERVER1 column.
I then compared those to SERVER2, the second server that has stopped reporting in, BUT has FULL McTray information. It also had patches installed the same day, but there is a difference of three less on SERVER2 than SERVER1.
I then went to two other servers (SERVER 3 and 4) that are having NO problems whatsoever. Same patches as SERVER2, except they were installed in a different day.
I'm still looking elsewhere.