We were having the same problem in our GIS lab with most of the computers. They all came from the same image but some of them didn't work. Windows 10 with arcgis 10.4. There was a red x next to the input box even in a blank document without any data. Trying to run the tool gave a blank error box with no description as to what was causing the error. DOING THE REPAIR FIXED IT. Thank you @Martin Leavitt
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