Unable to add mapped domain name

Working fine now but would like to know what it was all about!
(The above line was added five minutes after I posted the problem below)
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Hi ya!
I used the domain mapping plugin with no problem before but this time there's a problem with adding the mapped domain name for a network site. Here's my checklist:

1. A static IP is assigned to my main site.
2. This IP resolves fine when typed in the browser address bar.
3. The plugin has been installed correctly with sunrise.php under the wp-content folder and the extra line in config.php is in place in the right place.
4. The IP has been assigned on the settings screen of the plugin.
5. The domain to be mapped has been parked at the registrar and an A record has been assigned.
6. This change has propagated as when I try to access the domain name to be mapped it resolves to the IP of the main site.
7. When I try to map this domain to one of the network sites I type the domain name on the settings page and click the add button but nothing happens. The domain field gets cleared and that's all. This is the problem.

I'm using WP 3.3.1.

Any ideas from down under ?

Thanks !