Circled Glyphs Script: No Attribute 'Masters'

I try to build Circled Numbers with the MB Script Build Circled Glyphs (latest Version). At first it didn’t work because i had no stem values, now I get an error because 'objc.native_selector' object has no attribute 'masters'. I Could’t find the issue in the forum. At first I thought it was a problem with the (non existing) Custom Parameters, but could’t figure it out. What is a master attribute anyway?
Thanks in advance.