I figured out what caused the error, but don´t understand. after installing the DTS script for SSS mental ray stoped working. it worked quite well in the past so I didn´t connect this script with the error. but it happend that after adding the DTS plugin a file called maya.rayrc showed up in the local prefs folder (maybe it has been there before, I don´t know). but after removing it MR does its job fine again.

updates coming next.