ExtendedIllegalArgumentException: parameterList: Parameter value is not valid in ProgramCall.run()

I'm just trying for the first time to call a system API (QTNADDCR) using
PCML and a ProgramCallDocument object.  The PCML parses OK, but I get:

        com.ibm.as400.access.ExtendedIllegalArgumentException:
parameterList: Parameter value is not valid

on the ProgramCallDocument.callProgram( programName ) method.

I've tried setting com.ibm.as400.data.PcmlMessageLog.setTraceEnabled(
true ).  This gives some parameter information, but it seems to only
show the parameters that I initialise with the "init" attribute in the
PCML.  That said, when I tried initialising _all_ the parameters that
way, instead of setting them in the Java code, it _still_ only showed
the two parameters that I originally initialised.  This made me wonder
if it was showing the parameters that were in error, but one is a
one-character flag which I've set to "N", and the other is a (seemingly)
arbitrary ten characters.

This stuff seems to be too obscure for any web search that I can
construct to help, so I hope somebody here can give me some pointers:
how can I find out what's wrong with my parameters?

FYI, the API has an optional parameter, which I'm not specifying.
Tomorrow I might try including that, though if it's really optional...

Cheers,

Martin.

--
Martin McCallion
Senior Technical Consultant
Work:  martin.mccallion@misys.com
Home: martin.mccallion@ukonline.co.uk
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