Following the release of OS X Lion, Parallels issued a few updates for its "Parallels Desktop" virtualization software that allows Windows and other operating systems to be run in tandem with OS X. The latest update for Parallels 6 and Parallels Server (both version 4.0 and the Mac Mini edition) will run on Lion, so if you have these products be sure to install these updates if you have upgraded to Lion.
Parallels encourages people who are upgrading to Lion to keep their Parallels Desktop installations at the latest versions. While older builds and versions of the software may launch and perform in Lion, Parallels is only supporting the latest version of Parallels Desktop 6 in Lion. If you currently have Parallels Desktop version 4 or 5, then you can upgrade to version 6 for $39.99 "for a limited time," according to Parallels.
To update your Parallels installation, choose Check for Updates... from the Parallels menu to run the Parallels updater, and install the latest build, which is build number 12094 and will be around 207MB in size. After installing the update, your virtual machines will need to be updated with the latest Parallels Tools packages to ensure full compatibility.