CPU OVERLOAD error 6101 HELP

[hotel17]

Bought Pro Tools 10 2 weeks ago. Use it on my iMac 3,1Ghz i5 8Gb Ram and MBA 1,8Ghz i5 8Gb. Use a Motu 4pre.

I haven't been able to record 1 minute of music due to CPU OVERLOAD error 6101. I'm truying to record my guitar to a mono track, with no inserts, no plugins, no effects whatsoever: after a few seconds of recording I get the error message. Even when I don't use my Motu interface and try to record with the Pro Tools aggregate device (built-in mic) I constantly receive an error message.

At first my Host Processor was set to 4 processors, then to 3, then 2, ...
nothing is helping.

never had this problem. Ableton Live, Garageband: al work perfect.
Thought I bought thé industry standard for audio recording :-(

can someone help me out?