Hi Henrik,
When I first did it, I did get a response error saying something along the lines of "file character missing at line 2" which was a weird error.
I've discovered a new error that causes SOAPUI to crash on itself and not recover:
Since I am doing a datasource loop (excel file contains path of files to upload on each webservice call), when I go back and view each response, it crashes. Why? because the files I am uploading at 5MB to 100MB (depending on calls) large. By accident, i clicked on "request" of say WS call #4 (11MB) file, SOAPUI closes itself and all work is lost. It is because in the data node, it's trying to put all the data in there and it explodes in the viewer.