Most of the Parallels Desktop 6 users are experiencing an issue not finding the virtual machine windows after upgrading to Mac OSX Lion. This might be caused by the Desktop (inwhich Parallels to run on) being set to
None during upgrade. Mission Control to blame? But this can be fixed very easily. Follow these steps,
Options. Then set
According to Parallels FAQ, there is one more workaround to fix this issue,
I hope this will be helpful for those struggling to get around this issue.