Canon 7D issue

[Kerro]

My Canon 7D seems to have developed an issue lately.
When I am in any of the manual modes, when I press the shutter button I
have to press it again to take the shot. In either Auto mode it works fine.
I think I may have inadvertantly changed a setting and damned if I can find
which one.
It was working fine last time I used it 2 weeks ago. Any ideas would be
much appreciated, as it's a pain to operate like this.

[Jules]

Check to see if you've enabled the mirror lockup function Kerro, that might be the issue.

[Kerro]

Jules, you are a genius. Mirror lockup was the problem. Thanks very much.