Screenlock and Video Camera

Hi, I'm having a problem with my BB 8900 when I try to use the video camera.

What happens is that the screen locks after a minute (I think) and I dont know how to diable this or change the screenlock settings. Actually there seems to be none. When the screen locks, the video camera automatically stops recording, and sometimes is left in a format that is unreadable (I assume corrupted).

I have a media card and therefore can take a few minutes of video but the screenlock defeats this purpose.

Any advice here? Thanks.