Community Builder broken in the admin console...

Had a very strange fault today whilst working on a community builder Joomla site. I had a version of the site on 2 different servers. Both working fine but the sites were using Community Builder 1.1.x, which had a security warning. So 1 upgrade later, both sites are fine again and running 1.2.1

But this was only the front-end. In the Joomla backend of one site none of the action icons for community builder were showing. There was a text hyperlink in their place, but clicking them had no effect. Creating a new user was impossible as the save button had no effect.

So, I had one site 100% fine and another with the problems in the admin console.

I assumed something had corrupted during the upgrade of the problem site so I had a sniff around:

Copied both sites my machine. Ran a diff. Everything the same.

Got a MySQL dump off both sites. Ran a diff. Both the same.

Running out of options now, filesystem and db are the same.

Permissions? Checked ok.

PHP version? Ahhhh - ok site running under PHP5, problem site with PHP4.

Kicking the server onto PHP5 sorted it. This is bound to be a requirement stated in the CB docs, which I must of missed.

So make mental note - community builder backend only works in PHP5. I don't mind this, PHP5 is wayyy superior to 4. Upgrade all servers now!