All day WMV stuttery

Hi folks

My all day video is stuttery, its ok for for a while then part way through it starts to stutter
its done this for quite a long time now…

I am using 640x480 images from 4am to 10pm, its the same with video last day as well
PLease see the videos here to see what i mean, last hour appears to be ok, but yesterday
and lastday are not, sadly you need to watch about 4 hours into the video then thats it all
the way through, stutter stutter… ok, its not overly bad but i would have liked it to be smooth
again, I have a feeling it started when i changed from 352x288 to 640x480 but i dont want to
go back to the smaller image…

Any thoughts or ideas please…?