Could it be that you need to configure Silverlight settings in IIS? The Upload control that we're using for videos upload is Silverlight based. Please review this article
(bottom of the page) from our Installation and Administration guide to get abetter idea on how to configure your project properly. If the problems persist, please let us know.
the Telerik team
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items