I have got this error when tried to make slope less than 20 degree through Raster Calculator. One day before I installed Python 2.7.13 and after, this error appeared. When I delete the downloaded python, ArcGIS is not opening at all. Could it be the reason for the program not working properly?
ArcGIS Desktop installs its own copy of Python, usually in
C:\Python27\ArcGIS10.3. If you have installed your own download of Python it probably installed directly into
C:\Python27 and any Python paths in the Windows settings may have been updated into this location.
This will stop arcpy from working. To get arcpy to work again you can do a repair install of ArcGIS Desktop which will fix the paths for arcpy.
This happened to me the other day, a repair didn't take long and everything worked normally again afterwards.