You need to install Parallels Tool from the Virtual Machine menu to be able to use Coherence. Reinstall them if you already have PT installed
For me it did not work (even reinstalling PT). Incidentally, how would it work? I thought the windows of the Windows 8 would be on the desktop of the Mountain Lion.
I tried again and gets "The virtual machine display configuration could not be applied. Please try again or contact the Parallels support team for assistance."
I tried again, and again, and again. The error was fixed, but coherence don't works. I followed the guidance that support gave me for chat and neither worked. [sorry for my wrong English]