AjaxSubmitLink doesn't work with multipart forms on Google Chrome.
AjaxSubmitLink calls wicketSubmitFormById in its onClick handler. When submiting multipart form this function creates hidden iframe and attaches handleMultipartComplete function to the onload event.
handleMultipartComplete calls loadedCallback with envelope parameter. On Google Chrome envelope is undefined so loadedCallback craches ("Could not find root <ajax-response> element" is reported).
I dig more and I found that handleMultipartComplete is called before server side callback completes, thats why 'envelope' is undefined....