Why won't this CREATE FUNCTION command work?

We have this function, which is written in RPGLE in the form of a module in
a service program. The following CREATE FUNCTION works fine on our v7r1
system and our v5r4 system. However, when we run it on our client alpha
test site (also v5r4), it fails.

CREATE FUNCTION LIBRARY/DT2ISOSRV (
TESTVALUE VARCHAR(50) ,
DATEFMT VARCHAR(4) )
RETURNS DATE
LANGUAGE RPGLE
SPECIFIC LIBRARY/DT2ISOSRV
NOT DETERMINISTIC
NO SQL
CALLED ON NULL INPUT
NO EXTERNAL ACTION
NOT FENCED
EXTERNAL NAME DATE2ISO(DATE2ISO)
PARAMETER STYLE GENERAL ;

Here's the error...
Token ( was not valid. Valid tokens: IS NO NOT NULL ALLOW FINAL READ

The cursor is positioned on the left paren in the second to last line of the
command.

This specification is necessary to identify the procedure and service
program name when the parameter style is general. The service program is
named DATE2ISO and the procedure in that service program is DATE2ISO. The
function, when used in embedded SQL statements, is DT2ISOSRV. Like I said,
it works on two different systems. But not on our alpha site.

Any ideas what could be different between the systems? This is a
showstopper for us.

Best Regards,

Thomas Garvey