If a LISTLOG shows the following:
REXX090E SYSEXEC ddname is open and can not be modified
REXX084E REXXLIB allocation/concatenation process failed
This indicates the SYSEXEC is open, so it can't add to the concatenation. Add a close statement similar to the following to execute when logging into to SYSVIEW.
TSO 'EXECUTIL EXECDD(CLOSE)' closes SYSEXEC
This will close the SYSEXEC, allowing dynamic addition to the concatenation.