RunScript called for a non-script addon?

I get the “RunScript called for a non-script addon ‘script.module.stiff’. This behaviour is deprecated.” for the following plugin – what’s wrong about t?

Code:
<?xml version="1.0" encoding="utf-8" standalone="yes" ?>
- <addon id="script.module.stiff" name="stiff" version="0.0.1" provider-name="stiffauthor">
- <requires>
  <import addon="xbmc.python" version="2.25.0" />
  </requires>
  <extension point="xbmc.python.module" library="addon.py" />
- <extension point="xbmc.addon.metadata">
  <summary>Stiff skin support module</summary>
  <description>Stiff skin support module</description>
  <platform>all</platform>
  <license>ala</license>
  </extension>
  </addon>