Disperse Markers tool: Error 000200 Reference Scale Not Defined

[DylanHorsch]

I am attempting to disperse overlapping points in a single layer file - multiple data points for the same location across time - using the disperse markers tool. I am receiving the above error, even after setting the reference scale. I have attached a screenshot as well. Could it be a formatting or syntax issue? 

[Chris_French_WSP]

Instead of inputting '1:10,000' as the reference scale, try '10000' instead. It might be a formatting problem.