I'd be interested in knowing which process is tying up the port.
Is there anything additional in the logs?
/var/log/httpd/error_log
/var/log/low_level_service_watcher
You may want to try the following:
1. # amp_disable
2. # service httpd restart
3. # service pound restart
4. # amp_enable
---------> this method restarts the web servers used by AMP, hopefully releasing and renewing the port.
If that doesn't work and you don't care about root cause, a server reboot would definitely do the trick to release the port for apache (may have to issue another amp_enable after a reboot).