I had the same error a few weeks ago when I tried to use a buffer tool. Out of curiosity, I checked some other geoprocessing tools and then I realized that tools like merge and union have the same error. I have tried every single remedy and solution (except uninstall/change option) I could find here and on the gis.stackexchange website, but nothing did not help. In the end, I was left with only one solution. Control Panel > uninstall / change programs > right click ArcMap > Uninstall/Change > I choose to repair software and everything is working well now. In my case, this was the only way to fix this issue. Best Regards, Maja
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