Handbrake help?

I just downloaded handbrake 0.9.1 (i have 10.4 OS) to convert some 3gp videos from my blackberry to mp4s so i can edit in imovie.
When i open handbrake and select the file i want to convert it says 'not a valid source'. I tried opening virtually every movie file on my computer and still get the same message.
what am I doing wrong? do i need to change some settings, please help.

The problem lies in the version of Handbrake.
It didn't support 3gp until 0.9.3., so I don't know how you can get around that.
ffmpegx will convert it and work on your OS, but it's not great for quality on this format.