What is the contents of your $INFORMIX/etc/sqlhosts file?
What are the values of DBSERVERNAME and DBSERVERALIAS in your $INFORMIXDIR/etc/$ONCONFIG?
What is the value of
Are you sure this port is not in use by another application?
Could you try and set
sqlexec 8000/tcp in your /etc/services file and try to connect to that port?
I don't have any AIX boxes so I cannot check what the os errnumber 72 means.
You could always check your errno.h file on your aix box.