If you bought the retail copy of Parallels Desktop, and have a Mac Pro or a Core 2 Duo-based Mac (iMac, new MacBook Pros), it is highly recommended that you upgrade to Build #1970 of Parallels Desktop. This thread by Andrew at the Parallels support forum explains why:
There are a lot of complains from Mac Pro and newest Core 2 Duo Mac users about kernel panics or “grayed screen with different languages” on virtual machine startup.
The problem in using old Parallels Desktop Build 1848 (or 1848.2) which was released prior to Apple announce of Mac Pro and Core 2 Duo Macs and it is not compatible with these Macs.
Unfortunately this build is still available in retail stores (even in Apple stores) and staff is not aware of this problem.
If you have any problems with old retail version of Parallels Desktop – please upgrade it on build 1970! It can be freely download from our web site – http://www.parallels.com/en/download/desktop/ . Your permanent registration key will work with this version.