I have created a simple custom block for adding quotes, citation and links but the new block does not display in the Add Functionality area.

I have created blocks before, but this is the first time in version 5.4.2.2

What sort of things could prevent a block showing up?

I have added all of the required files to the top level 'blocks' folder, including icon, db.xml, add, edit, etc etc

I have also logged out, and in. Cleared the cache. Stopped and started Apache / mySQL, etc but nothing shows up in the Add Functionality area.

Any help would be most appreciated.

Gav