Ajax error when using date type widget with convertor variant="datetime" under ajax mode in Form

[lingerer]

Hi,developers
    This error can be reproduced by modified samples files under
build\webapp\samples\blocks\forms\forms\form1_template.xml
    1.Change <ft:form-template action="#{$cocoon/continuation/id}.continue"
method="POST"> to <ft:form-template
action="#{$cocoon/continuation/id}.continue" method="POST" ajax="true">
    2.Delete all repeater display to avoid repeater error under ajax mode
    3.Access http://localhost:8888/samples/blocks/forms/form1.flow ,click
"submit".
    A dojo dialog will apear shows "Requested Fail"
   The dodo console will show:
DEBUG:  got response using: XMLHTTPTransport
DEBUG:  XMLHttpTransport error callback failed: [object Error]

This error only appear under ajax mode.Both IE and FF will be affected.
Cocoon version is 2.1.11

Roy Huang