Hasta La Motion!

I have rendered out a half float exr sequence from maya 2009 along with various other passes. When I view the beauty pass in Nuke viewport there are strange square coloured pixles scattered around each frame. These artifacts are also visible when I write out to a different format so the random pixels must be in the original renders. Has anyone ever had this problem and if so you know what causes it? as a note im not getting these artifacts on any of the other render layers such as vector or zdepth…