UNHANDLED EXCEPTION: UPdating material

Line 1339 Preparing camera sample
i get this error with randomish maps in my scene. I have been through my scene making all the maps smaller to save ram usuage, but I stil get these errors.
I also cant select my main multisub material for my site. I t contains 40 odd materials, and ons elction i get this same message and all the previews of the materials scramble.
any ideas?

tim

edit * one other thing is that I dont even have the maps selected to render. I have a global override white material, yet I still get the errors.

max 7.5 and latest build

another edit * infact I cant seem to render with everyhting turned off. AA, lights, the works, loads maps then bam, same error

ok, it works on another machine and on the renderfarm.
i have cleared another gb on my C, incase that was an issue. now im just stumped