'XML5619: Incorrect document syntax. ' error in IE10 Only
set the content-type of you're request to text/xml and the error will disappear.
I think IE10 expects the content-type to be set. Check Developer tools -> Network -> Start capturing what type your request is.
For Ext.Ajax.request set the content-type to application/json.
XML5619: Incorrect document syntax.
Above issue throws in IE because the Content-Type wont be there in the response header. To cross check the same, Open Developer Tools >Network check Content-Type for the request that will be black. IE expect Content-Type for every response data. To solve this issue set the content type for the response