can't get ontape to work

Help I am bewildered by something I've done a million times. I am working on upgrading in aix from ids 10 to 11.5. Trying to do a quick ontape of a small instance before upgrading. I am in my old INFORMIXDIR ( the 10 version ) I set the ONCONFIG to a directory and file for TAPEDEV. I chown informix:informix and chmod 660 ( tried 666, 777 etc.. ) to the file. No matter what I do, even if Informix owns the directory, whenever I issue the ontape command ontape -s -L 0, it I keep gettting: could not write archive tape. What the heck is going on !! It's got to be something so overwhelmingly simple that I am brain farting on. I have installed the 11.5 software, but I am not pointing to it at all, and can't see how that can affect this, but who knows. Thanks.