I'm actually having the same problem or some thing very similar. I'm also running the web-service GetRunningWorkflowTasksForCurrentUser when the form is opened, based on the condition that the url is not blank. This form was working correctly until two days ago, but I have the same problem of TTest when open the form to respond a task, even publishing old backups of the workflow and the form that worked out.
As I have a Debug section in my form, I can see, if select the option "continue" in the error message, that the fields from this web-services are blank. I'm not pretty sure, but as I was informed there is a problem with permissions as in the server logs it was acused the 401 error.
Thanks in advance.