The core:arg tag was enabled, but we are still receive the error:
BPM-0704: An error occurred while executing custom script: com.niku.union.gel.GELValidationException; lineNumber: 60; columnNumber: 71; Environmental tag restrictions are in place. Tag 'arg' is not registered for use in this system. at com.niku.union.gel.GELValidator.startElement(GELValidator.java:142) ...
Release : 16.0.1
This error is specific to FedRAMP environments, which have Gel tag restrictions enabled.
The arg tag wasn't actually a problem, it was related to this other tag, and we were getting a false positive error on the wrong tag.
It's recommended to review and compare the tags referred to in the GEL script, and ensure all the tags usedare allowed, not just the specific tag noted in the error.