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FF/RWD tend to be "buggy" with most decoders. Try using skip instead. If you do, then you can set in configure how much to skip for each press. I think default is 1 minute ahead and 30 seconds back. If you press "4" and skip forward, then gbpvr will skip 4 minutes ahead.
If FF/RWD gives you problem, it's recommended you set, in config, "use short skip" instead of FF/RWD (I can't remember the exact phrasing right now).
I'm not always right
Accent HT-400 Case, AMD Athlon 64 3800+ 1024MB, 1TB+300GB+180GB, WinXP Pro-SP2, NVidia 7600GT
Nova-T USB2, PVR-350 recording from Dilog 355 DVB-T box, USB-UIRT (receiving & transmitting)