I see the oldPath has "ä" in the name. Python normally doesn't like that and other functions may not work well with these type of characters (for instance working with the raster calculator). Personally I would reconsider if the path should be named like this (also spaces, points, dashes, etc will be a sources or problems when working with rasters calculations).
oldPath = r"R:\natura 2000\8847.04 MaP\7218-341_Calwer_Heckengäu"
You may have to use the next line as first line in your script:
# -*- coding: utf-8 -*-
If that doesn't work, maybe you should enclose your script by:
import sys
reload(sys)
# read system settings and set utf8
def_enc = sys.getdefaultencoding()
sys.setdefaultencoding('utf8')
# script logic goes here ...
# restore settings
sys.setdefaultencoding(def_enc)
But my recommendation is to reconsider the folder names