occlusion artifacts with Renderman for Maya

[marcbnt]

hi,

I'm trying to render occlusion with renderman for maya, but I keep getting artifacts:

http://members.lycos.nl/marcbnt/rfm.jpg

I even get these artifacts while rendering the example scenes included with rfm the documents.
Increasing Samples, decreasing Max Variation or Shading Rate doesn't solve the problem. Any ideas? Some parameter I forgot?

Thanks in advance

Marc

[Westsidazrhidaz]

try increasing the trace bias under Raytracing in render globals

edit: well it worked just yesterday but now im getting the artifacts again.??