The Rule IsNotMRAManager doesn't looks to be an OOTB rule (please correct me if i am wrong) and the rule must have been created the when rule in some other class(for ex. implemetation class).
But this rule pyCreateCaseMenu is in Data-Portal class and in UI-Kit ruleset.
One option to test the change that you are trying to perform is save this rule(pyCreateCaseMenu) in your ruleset and save the when rule in the Rule-Obj-Flow class. Then try to use the when rule in this Navigation rule saved in your ruleset. This should allow you to save and test this modification.
On my Pega 8.2.2 system, I opened "Data-Portal pyCreateCaseMenu UI-Kit-7:13-01-01" and did a private edit, and then tried to save it. I got the same error. So, it seems that something is wrong for this rule. See attached screen shot.
Please raise a SR for it. We will do further investigation on it.