First of all, your command is syntactically incorrect. It should be:
grant OBLAH_DEE to "OBLAH_DAH" IDENTIFIED BY "15gx9FR7GG";
The problem with that: you can not grant password protected roles to another role. See https://support.oracle.com/epmos/faces/DocContentDisplay?id=1663997.1 for details.
ERROR
-----------------------
ORA-28405: cannot grant secure role to a role
...
Starting With Oracle 11.2.0.4.0 and 12c granting secure or password
protected role to any role (normal or password protected) we raise
this expected error.
grant::=

grant_system_privileges::=

grantee_identified_by:

As you can see in the 3rd picture, when using the IDENTIFIED BY
clasue, the grantee can be only an user, but not a role. (By the way, that clasue is used for something else.) Using the regular grantee_clause
, this is the error you would receive:
SQL> create role r1;
Role created.
SQL> create role r2 identified by 1;
Role created.
SQL> grant r2 to r1;
grant r2 to r1
*
ERROR at line 1:
ORA-28405: cannot grant secure role to a role
And what you tried:
SQL> grant r2 to r1 identified by 1;
grant r2 to r1 identified by 1
*
ERROR at line 1:
ORA-01920: user name 'R1' conflicts with another user or role name
As a workaround, the below parameter can be set to revert to the old behaviour:
alter system set "_grant_secure_role"=true scope=spfile;
You must restart the database for the change to take effect.