bet.com broadcasts RTMP flash video streams. Replay AV doesn't support them.

Replay Media Catcher works fine for me. Try to start recording with it and only then open your browser and navigate to a web-page from you which you wanna record.

Some more tips on recording RTMP streams:
How to record/download/capture/save Macromedia/Adobe Flash .FLV video RTMP stream from embedded player