I'm also using the CommerceQuest Queue Tool and faced the same issue when upgrading from MQ V6 to V7. After some unsuccessfull testing did I a last try that at least worked for me. I created the below ...
Check the MCAUSER on the SYSTEM.ADMIN.SVRCONN channel on the AS/400. If it is *PUBLIC you will not have any access to the qmgr. If it is blank the MCA will use the userid you are signed on with on you ...
Try this sample that I've created. It contain some specialites for ILE/RPG such as call to C-function memmove from the RPG program.
I send you the source code as attachment in an em.