Issue with SYSTABLES in V5R3 and OPNQRYF

We are having a strange error, during a test on V5R3 with the
SYSTABLES file. Any suggestions are welcome,.

We are using old code that worked fine on V4R4. The client is testing on V5R3 

Message . . . . :   Shared open of member SYSTABLES failed.              
Cause . . . . . :   The shared open of member SYSTABLES file SYSTABLES in
  library QSYS2 failed because of error code 6.
6 -- The process large object fields specified in the program is not
consistent with
the value specified for the original open. 
 
The code looks like this:
                                                                      
            CHGVAR     VAR(&QRYSLT) VALUE('TYPE="P" *AND WKFCHR="W" +
                         *AND SYS_DNAME="' *TCAT &DTALIB *CAT '"')   
            OVRDBF     FILE(SYSTABLES) LVLCHK(*NO) SHARE(*YES)       
            OPNQRYF    FILE((SYSTABLES)) QRYSLT(&QRYSLT) +           
                         MAPFLD((WKFCHR '%SST(SYS_TNAME 6 1)'))      
                                                                     
* READ THRU OUTFILE & RMV ALL MBRS FOR WORK FILES */                 
                                                                     
READ:       RCVF                                                     
 
The RCVF is where the error occurs.

Thanks

Krish