APEX

Hi together,

My challenge is to start an OWB workflow from an apex procedure.

Procedure:
declare
numb number;
audit_id number;
begin
numb := rtruser_blueprint.exec_api.execute('LOC_A014_OWF_MGR', 'PROCESS', 'LOAD_CALM_DELIVERY', ',', 'DELIVERY_ID_IN=6', audit_id);
end;

My problem is the following error:
ORA-06565: cannot execute SET ROLE from within stored procedure

This error occures at the following row in the execute-Procedure in the package exec_api (standard owb execution package):
dbms_session.SET_ROLE('OWB_D_rtr10201_blueprint');
dbms_session.SET_ROLE('OWB_O_rtr10201_blueprint');

If I run this script directly with sqlplus, the procedure works fine. As a result of this, I assume, the problem has to do with the grants which the apex execution user (APEX_PUBLIC_USER) doesn't have in contrast to the blueprint user (which is schema owner)

More informations about the environment setup:
The apex workspace is bound to the database - user: BLUEPRINT.
BLUEPRINT has the grant to execute the procedure 'EXECUTE' in the package 'EXEC_API'. The 'EXEC_API' package belongs to the user 'RTRUSER_BLUEPRINT'.

My concrete question is: Which rights / grants does which user need to execute the procedure directly from APEX?

Thanks for your help!

Mirco