I have downloaded and installed Windows 7 beta 7000 on my PC from Microsoft.com for a few days. Today,I got the bluescreen when doing this below.

Go to the "Windows Color and Appearance". and then Select the Active Title Bar in Item drop-list. Now, type the number 9999....(hold on the number key 9) in Size. You know what will be happenning.

Maybe it's bug of OS or not. Same thing happened in the earlier testing version of Windows 7.