If you try to run the SNMP Poller and see the following error after clicking add OID, check the apache error log:

Alert: Unexpected error initializing OID tree; check logs

If you see a message similar to the following in the apache logs, follow the step below:

[Mon Aug 06 20:49:10 2012] [error] [client xxx.xxx.xxx.xxx] proxy: DNS lookup failure for: localhost.localdomain returned by /uptime/snmp/getMibTree, referer: http://xxx.xxx.xxx.xxx:9999/main.php?page=SnmpPoller&subsection=Add&erdcBaseId=79

Check the apache http.conf file to see what is listed for the Proxy settings and compare those against the settings in the uptime.conf file.

Example http.conf:
ProxyPass /uptime http://localhost.localdomain:9996/uptime retry=0
ProxyPassReverse /uptime http://localhost.localdomain:9996/uptime
Example uptime.conf:

In this case, the localhost.localdomain was causing the issue.  By changing the setting to localhost, the error went away