Can anyone help?

I am playing TA and for some reason when I try doing a screenshot the screenshot is completely black

I am running the game on Windows 7 (saved from Windows XP older PC) on bootcamp on my iMac and have had to download an application to run screenshots called Gadwin Printscreen which seems to work fine print screening other stuff but not the screens from TA for some reason (this is because the screenshot function doesn't seem to work on my smaller Mac keyboard as there is no F13 key...)

My iMac is almost brand new so I cant think it's a video driver issue

Any help appreciated as this is stopping me writing my AAR for my game...