Hello ,
Our environment is
AIX 4.3.3 ML 1O
INFORMIX 9.21
traying to connect we have the following problem :

listener-thread: err = -25573: oserr = 72: errstr = : Network driver
cannot accept a connection on the port.
Please give us any help to perform this situation

Is your sqlhosts file setup?

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
INFORMIXDIR
INFORMIXSERVER
INFORMIXSQLHOSTS

What port did you define in /etc/services?

Hello
Thank you for give same attention to my problem.
What is the contents of your $INFORMIX/etc/sqlhosts file?
ibmpt onsoctcp ibmpt sqlexec

What are the values of DBSERVERNAME and in your $INFORMIXDIR/etc/$ONCONFIG?
ibmpt, DBSERVERALIAS not set

What is the value of
INFORMIXDIR -/users/informix
INFORMIXSERVER- ibmpt
INFORMIXSQLHOSTS not set

What port did you define in /etc/services? 2000

best regards

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.