Hello Elgg getting started group!

I have an install problem that seems to be a bug:

I'm installing on Ubuntu LAMP. The installer has found the database, the data folder (I assume) is correct it's above root and world writable.

I'm on the "System Settings" page and I've set the name of the Elgg site, the site email address, etc. etc.  When I try to save the settings, I get a 404 error saying

/Elgg/action/systemsettings/install was not found on this server

I looked in the files and the name of the folder is "actions" with an s, so I'm not suprised to get this error.

Anyone else have this problem?

Thanks for all your help.