Basically, when double clicking on a file in RadFileExplorer, the control is trying to open the file in the preview window which is a RadWindow control with a standard <iframe> element with src attribute pointing to the file to be diplayed - thus if the client's browser is able to display the file it should be displayed in the preview window as well.
From the filetypes that you have listed, only the wmv
files cannot be opened by the browser's out-of-the-box. The browser require appropriate plug-in (in this case WindowsMediaPlayer plug-in) to open specific files.
Could you please verify that such plugin is installed on the problematic machines? If so, and / or the second behavior (download dialog popups) occurs with different filetypes, could you please sample page along with problematic files that can reproduce the problem so we can investigate the issue further?
the Telerik team
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