I recently installed TightVNC, and used it to access my desktop from my phone. When I did so, my desktop reported that Aero had been disabled due to an application being run that didn't support it. I now cannot re-enable Aero, despite having closed the TightVNC server (and indeed having rebooted a number of times since).
Windows 7 troubleshooting reports the following:
Close programs using mirror drivers
To allow Aero effects to be displayed, close any programs that use mirror drivers (a type of display driver), such as Windows Remote Assistance and Windows Live Mesh.
The troubleshooting system appears to attempt to automatically fix that, but fails.
I can see nothing in the task manager that obviously uses mirror drivers; in particular, I can see nothing that looks like TightVNC in there. Starting and exiting TightVNC makes no difference.
Google has turned up nothing that looks useful so far, either, although my Google-fu isn't great and I may just be searching for the wrong things.
There's another question that reports the same problem, caused by LogMeIn rather than TightVNC, but the solution listed there doesn't work—TightVNC doesn't install LogMeIn mirror drivers, for obvious reasons.