I think you can try one of these options
1. Check your processes parameter value in init.ora, if this value is high enough check the AIX/ OS parameters, the max number of processes / user allowed, if this is small increase the processes value
2.increase the swap space may be the resources are not available to allow connections
3.if otrace is enabled disable that.
Stop the Oracle database.
b. Go to the $ORACLE_HOME/otrace/admin directory.
c. Delete all files with a '.dat' extension.
d. Restart the Oracle database.
1. Check your processes parameter value in init.ora, if this value is high enough check the AIX/ OS parameters, the max number of processes / user allowed, if this is small increase the processes value
2.increase the swap space may be the resources are not available to allow connections
3.if otrace is enabled disable that.
Stop the Oracle database.
b. Go to the $ORACLE_HOME/otrace/admin directory.
c. Delete all files with a '.dat' extension.
d. Restart the Oracle database.