Help creating new add-on

I have created, what I hope, is a simple addon. But when I try to "Install from zip", it returns "add-on does not have the correct structure".

I have tried on my main Ubuntu-based XBMC and also a test OS X-based XBMC too.

The add-on has the following structure, zipped up inside script.bashrunner.zip:

/script.bashrunner
addon.xml
default.py
mainscript.sh

The contents of addon.xml are:

Quote:<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<addon id="script.bashrunner" name="Bash Runner" version="0.1a" provider-name="me">
<requires>
<import addon="xbmc.python" version="2.1.0" />
</requires>
<extension point="xbmc.python.script" library="default.py">
<provides>executable</provides>
</extension>
<extension point="xbmc.addon.metadata">
<platform>linux osx</platform>
<summary lang="en">Core add-on to initiate bash scripts</summary>
</extension>
</addon>

This looks correct matched up against other add-ons I already have installed and using various forum threads where people are having issues with their own add-ons. I have zipped it up on both the Ubuntu and OS X PC's, so the .DS_Store directory has been deleted, and nothing else is inside it.