SQL> exec a
BEGIN a; END;

*
ERROR at line 1:
ORA-28575: unable to open RPC connection to external procedure agent
ORA-06512: at "FULCRUM.AACONVERTDF_R", line 0
ORA-06512: at "FULCRUM.A", line 8
ORA-06512: at line 1

ORA-28575: unable to open RPC connection to external procedure agent
 *Cause:   Initialization of a network connection to the extproc agent did
           not succeed. This problem can be caused by network problems,
           incorrect listener configuration, or incorrect transfer code.
 *Action:  Check listener configuration in LISTENER.ORA and TNSNAMES.ORA, or
           check Oracle Names Server.