Teradata 15 : Failure 5619 Role nesting exceeded single-level
Teradata only allows one level of role nesting, there's no workaround.

Either role_2 or is already granted to another role or role_1 has been granted another role.

role_a -- top level
   | 
role_b -- GRANT role_b TO role_a; this is ok, 1st nested level
   | 
role_c -- GRANT role_c T1O role_b; this will fail, 2nd nested level