I recently installed 10.8.1 and now cannot add a field to any shapefile. I was able to add one to the first shapefile, but as soon as I tried to add the second I get an error messages that states 'failed to add field to the table/feature class'. I have tried other feature classes and tried exporting a feature class to a new one, no luck. I then uninstalled 10.8.1 and reinstalled and still have the same issue. Everything worked fine while I was using 10.4.
Are you really adding fields to shape files or are you adding fields to a geodatabase feature class? How are you adding the field? With a tool or in arcpy? Can you provide a screen shot of the actual error the gets returned?
Yes, I am really adding a field to a shapefile.... The two feature classes I
was able to add a field, I now cannot
A shapefile and a feature class in a geodatabase are two entirely different data structures.
Unfortunately you image didn't get attached. You may want to start a tech support case for this one.