uniform increase in render times

[alkis]

hi all
i was rendering a very simple animation of an animated flag.
a very slight dolly of the camera ( barely noticeable) and flag animated with max cloth extension. no other geometry in the scene
render slave specs
vray 1.46.15 max 7
dual xeons 3.2
2gigRAM -3gb switch enabled
winxp sp2
the render times keep increasing on both machines for no reason
forgot to mention that the animation is rendered through backburner not locally.
in the image below you ll see what i mean.
in the circle you ll notice a sudden change of render times at frame290
thats because at that point i shut down backburner server on that machine and restarted it . after that the render time came back to normal but continued to increase frame by frame.

[img]ftp://80.176.192.46/images/render2-log-flag.jpg[/img]

any help would be greatly appreciated

heres it the file as well
ftp://80.176.192.46/images/ANIM-FLAG-01.zip
regards
alkis

[vlado]

I'll look at the scene, but I don't have the cloth extension here, so I don't know if I will be able to replicate your results.

Best regards,
Vlado

[vlado]

You have used the "Multiframe incremental" mode for the irradiance map; this is not recommended for animations with moving objects. Use the Single-frame mode and the render times will be constant.

Best regards,
Vlado

[alkis]

i m such an idiot
i could swear i put it back to single frame.
thanks a million anyway vlado