BP Rec activity means the number of times that BURN-Proof was activated. BURN-Proof is Plextor's method of preventing buffer underruns. This technology kicks in when your computer cannot supply the drive with enough data during the recording process. BURN-Proof then pauses the recording process until enough data is available again.
What are the specs of your computer? It could be that your computer is not fast enough to handle the recording speeds you have selected. Have you checked if DMA is enabled for your Plextor drive and your hard disks?
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