Symptoms
We are seeing the following error when we use a role as a destination in a client event: The parameter 'addresses' cannot be an empty string. Parameter name: addresses.
Diagnoses
This error normally presents itself when a email address is empty or malformed.
Resolution
After executing "UMUser" > "Get Role Users" smartobject method, we noticed that one of the user's email addresses was invalid/malformed. Once the email address was fixed, things were working as expected.