Windows 8.1 is not officially supported yet at this time. You can run the program by doing the following:
In Windows 8.1-
Open the 'Start' menu and select 'Desktop'
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Open a file browser.
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Navigate to 'Computer' in the file browser and open the folder 'C:\Revolution\R-Enterprise-6.2.1\IDE64 and double-click on the file 'RevoIDE.exe'.
You can create a Shortcut by right clicking on the file RevoIDE.exe and then dragging to the desktop.