Need help passing parameters from concurrent request to procedure

Application version 11.5.10.2 DB version 10g.

I have a concurrent program that has 4 required parameters. The concurrent program calls a SQL*Plus executable. Here's that executable...

DECLARE

  p_errbuf                 VARCHAR2(256);

  p_retcode                VARCHAR2(256);

  p_report_type            VARCHAR2(20);

  p_period_name            VARCHAR2(6);

  p_cad_to_usd_rate        NUMBER;

  p_override_prev_rate     VARCHAR2(3);

BEGIN

schema_name.proc_name(p_errbuf,p_retcode,p_report_type,p_period_name,p_cad_to_usd_rate,p_override_prev_rate);

END;

/

Here's the procedure...

CREATE OR REPLACE schema_name.proc_name (p_errbuf               OUT VARCHAR2,

                                                           p_retcode              OUT VARCHAR2,

                                                           p_report_type              VARCHAR2,

                                                           p_period_name              VARCHAR2,