Fire-i cams – drops of fps

Hello

I am using 2 Fire-i cameras chained on MacBook Pro osx 10.6.4
Max 5.1.5
images sent on GL slabs and effects (with colormode uyvy and the tricks you can find on the subject ;-)

I never had a problem before
The same patch I used 6 months ago (max v.5.1.3) worked fine.
Now the rate of the fps goes very low when something changes in front of the cameras.
The images sometimes fix for a moment

Anybody experienced that (I can’t reproduce on small patch and my GL patch is way to complexe now).