In general when working on scenarios with Ajax it's more convenient to use the RadAsyncUpload instead of the RadUpload as Richard had suggested. Nevertheless if you want to use the RadUpload you should disable the Ajax when the toolbar button is clicked as you are trying. In order to identify why you are not able to achieve the aforementioned action, please provide me the code that you are using so I could inspect it.
you could find a help article which is showing how to disable the ajax and perform a full post-back in scenarios like your.
All the best,
the Telerik team
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