Hello,
When loading this .ical file, I get error:
WeekDay can not be converted because of an unexpected value of the Day property:SU,SU.
Seems a bug in specific combinations of BYDAY and WKST parameters.
Also, a grammar thing, maybe you want to change the error string from “can not” to “cannot”, or better, CTRL+H to replace all instances in the project! 
Sample:
rfc5545.zip (1.3 KB)