We have verified that turning off the CuteWebUI.UploadModule prevents the problem from happening. The problem is, we use this module in other places in our application.
We have installed the latest version after this failed with an older version.
It appears to "intercept" the request (from a page that makes an XmlHttpRequest call -- this page does NOT use the AjaxUploader.
Successful Request (returns expected JSON body, has form data)
POST http://www.blah.com/ProjectTree.mvc/GetNodesByParent HTTP/1.1
x-requested-with: XMLHttpRequest
Accept-Language: en-us
Referer: http://www.blah.com/ProjectHierarchy.mvc
Accept: application/json, text/javascript, */*
Content-Type: application/x-www-form-urlencoded
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729; InfoPath.2; MS-RTC LM 8; .NET4.0C; .NET4.0E)
Host: www.blah.com
Content-Length: 19
Connection: Keep-Alive
Pragma: no-cache
Authorization: NTLM T...etc..F
Form Data: parentNodePath=ROOT
Failed Request (no form data)
POST http://www.blah.com/ProjectTree.mvc/GetNodesByParent HTTP/1.1
x-requested-with: XMLHttpRequest
Accept-Language: en-us
Referer: http://www.blah.com/ProjectHierarchy.mvc
Accept: application/json, text/javascript, */*
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729; InfoPath.2; MS-RTC LM 8; .NET4.0C; .NET4.0E)
Host: www.blah.com
Content-Length: 0
Connection: Keep-Alive
Pragma: no-cache
Authorization: NTLM T...etc...1
No Form Data
The Response for this Request looks like this
HTTP/1.1 200 OK
Date: Thu, 12 Aug 2010 18:23:52 GMT
Server: Microsoft-IIS/6.0
X-AspNet-Version: 4.0.30319
Cache-Control: private
Content-Type: text/html; charset=utf-8
Content-Length: 39
Error:Unable upload data via Flash+NTLM