We are getting error while submitting adaptive form.how to resolve this issue? i have attached complete error.log file . 

Client side we are getting popup with below error

[AF] [AEM-AF-901-004] Encountered an internal error while submitting the form

Error log details:

23.02.2017 15:37:52.829 *ERROR* [0:0:0:0:0:0:0:1 [1487844472814] POST /content/forms/af/qr/customer-care/jcr:content/guideContainer.af.internalsubmit.jsp HTTP/1.1] com.adobe.aemds.guide.utils.SubmitDataCollector Unable to create JSON for Submit
javax.xml.xpath.XPathExpressionException: javax.xml.transform.TransformerException: Unable to evaluate expression using this context