SOLUTION: Upload fails OR Login prompt appears when using Forms / Windows Authentication

[Telerik Admin]

Symptoms: A log-in prompt is presented to the user upon uploading files and the site uses Windows Authentication. If the site is configured with Forms Authentication the upload will fail without error message.

Cause: RadAsyncUpload will not send an authentication cookie when the end-user has Flash Installed.

Solution: Exclude the Telerik.Web.UI.WebResource.axd handler from authentication:

<location path="Telerik.Web.UI.WebResource.axd">
    <system.web>
        <authorization>
            <allow users="*" />
        </authorization>
    </system.web>
</location>

Note: Anonymous authentication must be enabled on the site for this workaround to work. If AA is disabled, you must disable the RadAsyncUpload Flash module altogether by inserting this script right before the control definition on the page:

<script type="text/javascript">
    Telerik.Web.UI.RadAsyncUpload.Modules.Flash.isAvailable = function() { return false; }
</script>

We're investigating the possibility to automatically send the authentication cookie.