Does anyone have any insight in to this?

Running this statement in isql:

EXECUTE PROCEDURE P_IMPORT;

Yields this error:

Statement failed, SQLCODE = -508
no current record for fetch operation
-violation of PRIMARY or UNIQUE KEY constraint

Yet running the same statement in Database Workbench yields no error.
The procedure is written to ignore unique_key_violation:

FOR SELECT
COL1, COL2 , ...
FROM
P_SELECT
INTO
:COL1, :COL2, ...
DO BEGIN

INSERT INTO
THE_TABLE (
COL1, COL2, ...
)
VALUES (
:COL1, :COL2, ...
);

WHEN GDSCODE unique_key_violation DO COL_1=NULL;

END