This is from Notebook Review and seems to solve the bootcamp and FileVault2 problem in Lion. Note: I had trouble installing Windows 7 Professional in Bootcamp AFTER having already enable FileVault2, which got me to do some searching.
If you are doing a new Windows install into bootcamp, whether or not your OS X installation is a fresh install of Lion or an upgrade from Snow Leopard, the key seems to be to have FileVault OFF, then install Windows, then install the Windows Support Software (aka bootcamp drivers that you burned or copied during bootcamp assistant) into Windows (this installs the latest bootcamp 4.0 drivers into Windows--remember Windows mounts the FileVault encrypted HFS+ volume of OS X when using Bootcamp), then make sure you can boot into either operating system, then finally turn on FileVault 2 in OS X, then make sure you can boot into both operating systems once more.
The link describes what to do if your getting blue screens in Windows, or reboots, or if you can only start Windows in Safe Mode. YOU NEED TO INSTALL THE LATEST BOOTCAMP DRIVERS INTO WINDOWS TO STOP THE BLUE SCREENS, follow directions on the link.
http://forum.notebookreview.com/apple-mac-os-x/597574-boot-camp-filevault-2-lion -watch-out.html