Hi JBessel,
It is probably due to the space set aside for your 'system restores' and is called 'shadow storage'. This amount is around 15% of your HDD if I remember correctly. You can modify this amount if you wish and I'll explain it as best I can.
If you right-click on 'command prompt' and hit 'run as administrator' a black box will appear. In the black box type this line copying the words and spaces exactly:
vssadmin Resize ShadowStorage /For=C: /On=C: /Maxsize=6000MB
Then hit enter. You'll notice that I've put the figure of 6000MB or 6GB, you can have any figure as long as it's more than 300MB as this is the size needed to properly save a system restore. I set mine to 6GB but you can change yours to whatever.. Also if your MBR is denoted by another letter other than C you'll have to change that also. Any problems please post back..
