Help me! Error -9128 on Pro Tools 10...

[poetagringoire]

Hello! I've got a problem with Pro Tools 10 with Windows 7 64 bit, Quad Core and 16 GB of RAM...
When I work with some virtual instruments, after about one hour i have this error, even if i don't change anything during this time:
“You are running out of CPU power. Remove some RTAS plug-ins or increase the CPU Usage Limit in the Playback Engine dialog. (-9128)”
I try to increase the cpu usage limit at 99% and i've clicked on "ignore errors during playback", but after about an hour i've too much clicks and pop... and i must restart Pro Tools, and then I can work again... I use only 2 processors and now I'm trying to increase the buffer size at 512... It's frustrating, because everytime i'm in the middle of an important pre-production work i must restart all... and i can notice the problem only after one hour! And this problem happens only when I've loaded virtual instruments, not during audio recording or mixing... Thank you so much!