serious problem

[phanipalagummi]

In middle of my stuff in ubuntu(7.10) my window gets black in color and it get stuck there(at this time only close button works),and later i need to close the window and reopen it,could any one give me the suggestions please.and why it is doing like this?more over i dont get any error just it stucks there.

[Trail]

If you have compiz enabled (desktop effects), the 'window' (which is it, by the way?) darkens to indicate that it is not responding.