What happened to my Reserved Variables?

["Ivory, Wayne" <wayne.ivory@ILUKA.COM>]

SQR 3
Informix 7.2(?)
SCO Open Server

We have an SQR that does a 'call system' to a Unix shell script and passes a
couple of SQR Reserved Variables to the script.  Recently this SQR has had
some major work done on it, and now the reserved variables appear to be
blank.  I'm not aware of anything that a programmer could do that would
affect this.  Following is the code:

            let $Run_String = getenv('PS_HOME') || '/../wsl_scripts/xferjnl
' || $USERNAME || ' ' || $OutputDest || ' 2>' || $SQR-REPORT || '.err'
            show $Run_String
            call system using $Run_String #Unix_Status

The 'show' produces the following:

            /u/peoplesoft/hrtest/../wsl_scripts/xferjnl  /tmp/GLIF9IM.1100
2>.err

Note that nothing is output where $USERNAME and $SQR-REPORT should be.  Yet
I wrote a 3-liner that says:

            begin-report
                        show $USERNAME
            end-report

which outputs 'HRTEST'.  What could be blanking these variables?

Wayne Ivory
Information Services
Iluka Resources Limited