Steam not quite working properly

Hi all,

This is a minor gripe but annoying anyway, so i thought i'd check if anyone knew a solution. When i'm playing a game on Steam (specifically tf2, not sure about some others), i can no longer bring up the community screen with ctrl-tab. It used to work, then stopped one day!
I've tried re-assigning it etc, and it doesnt seem to help. Very annoying since it means i cant chat to friends etc whilst playing.

Has anyone had a similar problem/have any good recommendations?

Thanks!