This is a generic java exception thrown when you attempt to re-read the contents of the input stream.
The processFormSubmission(Request, ...) method uses the HttpServletRequest Object which contains a ServletInputStream object in turn containing the posted data from your HTML form as binary data. processFormSubmission will try and read this a byte array.
If you have anything in your servlet/JSP code before the processFormSubmission which queries the contents of the request object, the InputStream will be parsed automatically and this exception occurs.
You have 2 options, 1) Make sure you do read the contents of the inputstream before calling processFormSubmission or 2) use the alternative method which takes a byte array instead of the Request object - the byte array would have to be manually created as name / value pairs of Http post data.
I would try and stick with option 1 but you may have no choice. BTW, This can also happen in struts based apps - same reason, but the framework is doing the damage.