That particular error appears to be associated with a corrupt xml file... WA_eCart/WA_DMCFG.xml
The ecart tries to store the design settings from your last application of the display manager.. that way the checkout wizard and displays added to other pages can automatically match. Somehow that file got corrupted and caused the error you are seeing.
Deleting that file and re-running the display manager should re-create the file and get around the error.