Need Assistance: CPU Overload Error

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I'm using a 2.4 Ghz MBP with 4gig RAM, 10.6.2 and PT LE 8.0.3.

I've got two vocals tracks with compressors and reverb, one with a de-esser, a kontakt drum track with reverb (no notes in the lanes, I was playing around with options), a mini grand track with a 4-band eq, and a master track with tl master meter, all in all not too heavy a session. When I play the track and go to put the 4 band eq in the piano track, I get a crackle and a cpu overload message (even though im only running at 25% before hand). My buffer is at 512 and my cpu limit is at 99%. MY RTAS PROCESSOR IS SET AT ONE (IS THIS STILL THE STANDARD THING TO DO?)

anyway, just wondering if there was something other than too low a playback buffer that could be causing this sudden spike of placing in an eq during playback. I'm suspicious of the RTAS processor but at least it used to be that 1 was the reccomendation (as opposed to 2) on the dual core mbps.

thanks guys!

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anyone? anything?