Found this online here: http://www.ubuntu-unleashed.com/2008/05/howto-fix-compiz-display-white-screen.html
Howto: Fix compiz display white screen when locked issue in Ubuntu Hardy Labels: Bugs, Compiz Fusion, Howto, Knowledge Posted by defcon on Tuesday, May 13, 2008 at 7:36 PM
Are you effected by this bug? Lets find out first: 1. Login to user 1 2. Use the fast user switcher applet to login to user 2 3. Logout from user 2 session
Result : You get a white screen. You have to type your password and the white screen will disappears.
or Try this: 1. Login. 2. Open a terminal and do "sleep 15 && zenity --question" 3. Hit Ctrl-Alt-F1 to get to a console. 4. Count to fifteen, slowly. 5. Hit Ctrl-Alt-F7 to get back to you gui session. Expected result: zenity should have put up a question dialog-box. Actual result: zenity's dialog-box is white.
If you get the following bug a fix has been released by Mario
Go to System --> Administration --> Software Sources and select the Third-Party Software tab. Click on Add and enter the following line: deb http://ppa.launchpad.net/superm1/ubuntu hardy main
Then click on Add again and enter the following line: deb-src http://ppa.launchpad.net/superm1/ubuntu hardy main
Click on Close, then on Reload. Shortly your software updater will indicate that there are updates available for compiz. Install them, restart your machine, and voila!
For more information on this fix and to follow the bug fix process please see bug 160264