Telerik version - 2011.1.614.35
RadAsyncUpload issues on Safari 5.1.7, IE 9 and Chrome 28.0.1500.95 -

Following is the list of issues seen on the mentioned browsers -
a.  On Safari, the upload file functionality doesn't work at all –
On Safari, when a file is selected from the Open dialog box, the dialog box closes and nothing happens after that. The file is not shown in the upload control, and no event is fired.

b.  On IE, the Open dialog box shows the specific file types by default, whereas on Chrome, all file types are shown by default –
We have set the ‘AllowedFileExtensions’ property of the RadAsyncUpload to “image/png,image/x-png,image/jpeg,image/pjpeg,image/gif,.x-png,.gif,.jpeg,.jpg,.png”. On IE 9, when the Open dialog box is opened, by default, the mentioned extensions as selected in the File Type drop down. Whereas, on Chrome, ‘All’ is shown in the File Type drop down. We would like this behavior to be consistent. Is it possible to show ‘All’ on IE9?

c.  On Chrome, uploading a file with size greater than the mentioned file size gives a Silverlight error (Refer SilverlightPluginError.png) –
i.	The MaxFileSize is set to 500 KB. When user tries to upload a file with size greater than 500 KB, the gets an alert message indicating he cannot upload a file beyond the said size. This works fine on all browsers other than Chrome. On Chrome, when a file with size greater than 500 KB is selected from the Open dialog box, the page seems to hang for some time. Then an alert message is displayed with following message –
The following plug-in is unresponsive: Unknown
Would you like to stop it?
ii.	Upon clicking ‘Yes’, following message is shown below the Chrome address bar 
Silverlight plug-in has crashed
iii.	And, the alert indicating file size greater than 500 KB cannot be uploaded is shown.

estoy utlizando radasyncupload  para una  webpart.  y requiero que cundo le de clic a un boton pueda acceden a los archos seleccionados pero al ingresar al evento  clic del boton el radasycnupload esta null, ademas que el evento FileUploaded nunca se ejecuta

We have created a KB article where a possible approach to achieve image resizing before the upload is suggested. You can find it at https://www.telerik.com/support/kb/aspnet-ajax/upload-(async)/details/resize-images-client-side-with-html5-before-uploading-with-radasyncupload

The article describes a straightforward way on how to change the uploaded image dimensions. You can further improve and modify the logic in the _uploadFile function to allow the user to define the new dimensions or use a tool to allow the users to modify the image.

Here's the scenario: 
User changes the extension of a .js file to .jpg and upload the file, by no means we are able to restrict the user from uploading the file. 
Is there a way to stop user from uploading based on associated mimetype ?

The user should be able to determine by which criteria the validation failed (size or extension).