There is a problem with uploading file which name contains greek, hebrew or russian letters. It is also replicated with other languages that contain non-latin letters, such as Japanese or Korean. 

Here are the steps to reproduce the problem.
1. Create text file "Καλώς ήλθατε.txt" and save it on local disc (file may contain any text).
2. Open http://demos.telerik.com/aspnet-ajax/cloud-upload/examples/overview/defaultcs.aspx
3. Click Select button and browse file "Καλώς ήλθατε.txt"
4. Message "Uploading Files 1/1" is displayed but file is not uploaded.
1. Create file Благодатное-небо-с-предстоящими.txt on local disc (file may contain any text).
2. Open http://demos.telerik.com/aspnet-ajax/cloud-upload/examples/overview/defaultcs.aspx
3. Click Select button and browse file Καλώς ήλθατε.txt
4. Message "Uploading Files 1/1" is displayed but file is not uploaded.



Here is the error from the console when trying to upload such a file:

Telerik.Web.UI.WebResource.axd?_TSM_HiddenField_=ctl00_QsfScriptManager_TSM&compress=1&_TSM_Combine…:6 Uncaught Error: Sys.ArgumentException: Cannot deserialize. The data does not correspond to valid JSON.
Parameter name: data
    at Function.Error.create (Telerik.Web.UI.WebResource.axd?_TSM_HiddenField_=ctl00_QsfScriptManager_TSM&compress=1&_TSM_Combine…:6)
    at Function.Error.argument (Telerik.Web.UI.WebResource.axd?_TSM_HiddenField_=ctl00_QsfScriptManager_TSM&compress=1&_TSM_Combine…:6)
    at Function.Sys.Serialization.JavaScriptSerializer.deserialize (Telerik.Web.UI.WebResource.axd?_TSM_HiddenField_=ctl00_QsfScriptManager_TSM&compress=1&_TSM_Combine…:6)
    at c.RadCloudUpload.HandlerUploader._successfulResponseStatus (RadCloudUploadScripts.js:477)
    at XMLHttpRequest.p (RadCloudUploadScripts.js:463)