Have you double checked your Agent policy in ePO to have the system tray icon appear? I believe McAfee's defaul may not have it appear, but I may be incorrect in that assumption.
I have not touched the default policies.
However the tray icon is checked in the default policy, so this is not the reason.
I have to add, that the auto start works with Agent 22.214.171.1240 for that client most of the time.
Can there be any concurrency problem with other services?
I could narrow down the issue.
The mctray.exe is not starting, when after reboot I directly login with remote desktop to the client.
If I login with the same username first locally, the mctray.exe process starts.
Logging after that via remote desktop => the mctray.exe is running.
Although it seems Windows 7 related, other Services can start their tray processes without an issue.