Windows – Remote Desktop and Aero in Windows 7

There is a good reason for this. Aero uses a lot of alpha blending, which needs hardware acceleration to be performant. Even without a dedicated graphics card, the onboard graphics can process the layers much much quicker. Unfortunately, what that means is that the screen buffer gets handed over to the graphics chip, and the OS never sees the final rendered frames. If they're just being sent to the monitor, that's fine, but Aero depends to a certain extent on hardware acceleration. When VNC tries to run with Aero, it will have to kill some of the hardware acceleration and force the CPU to do rendering, so it can capture the screen state. This unfortunately can force Aero out.

I work for RealVNC, and we use a mirror driver to help address this somewhat by grabbing the draw commands before they're sent to the chip for compositing, and hold our own buffer. I know that UltraVNC uses a mirror driver too in some way, but I've not looked into their implementation. You could try ours! I suspect if the performance is just too low, there might not be a way to force Windows to do compositing and blending on the CPU.

For whatever reason, it thinks it's rendering with that mirror driver. It's possible that simply having it installed is enough to disable Aero - it might have hooks in place all the time even though you're not actually using it, which are enough to throw Windows off.

You could disable the mirror driver in Device Manager, or entirely uninstall the remote software. Of course, this will inhibit your remote functionality, so it's a tradeoff.