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Apply all available updates to Windows and Internet Explorer.
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look into the Windows control panel - Software and deinstall ’ Visual C++ Redistributable for Visual Studio 2015 (x86)’
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reboot Windows
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download and install https://www.microsoft.com/en-US/download/details.aspx?id=48145
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re-download the installer .exe for Plex server (try a different web browser this time) and install it