there are various causes for this to appen. try exit the application and restart.. then try to ovverride materials.. and also you should give more information about your model, materials etc..
anyway there are a lot of discussions about this..

http://sketchucation.com/forums/search.php?keywords=encountered+error%28s%29+while+trying+to+render+error+log+details&fid%5B0%5D=322