Hello,
Take a look at the following KB article. It gives several different troubleshooting steps to help fix problems related to returning from sleep mode. One of the steps you can actually click on and it will make the registry changes for you.
http://support.microsoft.com/kb/929734
Does it say anthing besides "invalid mode"? Are you seeing the desktop when this error comes up, or is it a blue screen with a bunch of numbers and letters? If it is the blue screen, I'll need you to post the stop code that is listed.
Brent
Microsoft Answers Support Engineer
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