Commented Issue: AjaxFileUpload control not working on IE9, Win 7 [27177]

I'm developing a site on .Net 4 on Windows 7 32-bit in VS2010. I've updated to the May 2012 version of the toolkit and tried using the ImageUpload of the HtmlEditorExtender, but whenever I try upload an image, it just puts a red (error) next to the image name. I've tried giving Everyone full access to the folder where the image should be saved, but I cannot even see that it is getting to that point. I've also tried using just the AjaxFileUpload control to test it, but it does exactly the same. Any ideas?
Comments: $type.deserialize = function JavaScriptSerializer$deserialize(data, secure) { /// <summary locid="M:J#Sys.Serialization.JavaScriptSerializer.deserialize">Deserializes a JSON string.</summary> /// <param name="data" type="String">The JSON string to eval.</param> /// <param name="secure" type="Boolean" optional="true" mayBeNull="true">True if the method should perform JSON conformance checks before evaluating. False by default.</param> /// <returns>The results of eval applied to data.</returns> var e = Function._validateParams(arguments, [ {name: "data", type: String}, {name: "secure", type: Boolean, mayBeNull: true, optional: true} ]); if (e) throw e; if (!data.length) throw Error.argument('data', Sys.Res.cannotDeserializeEmptyString); var er, esc = Sys.Serialization.JavaScriptSerializer._esc; try { var exp = data.replace(esc.dateRegEx, "$1new Date($2)"); if (secure && esc.jsonRegEx.test(exp.replace(esc.jsonStringRegEx, ''))) throw null; return window.eval('(' + exp + ')'); } catch (er) { throw Error.argument('data', Sys.Res.cannotDeserializeInvalidJson); ///////////////////////////////Here the error occures \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ Uncaught Sys.ArgumentException: Sys.ArgumentException: Cannot deserialize. The data does not correspond to valid JSON. Parameter name: data \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\//////////////////////////////////////////////////////// } }