Sorry to hear that you are having trouble with your analysis! In order to figure out what is going on here, we need a bit more information. If possible, could you send us your data and we can try to repro it? If that isn't possible, can you send us some screenshots of your attribute table and the tool dialog right before you run it?
Again, sorry for the inconvenience! Hopefully we can get you up and running again soon!
Geoprocessing Product Engineer