ARGH!!!
Last one I swear ;-)
in the setup:
    includeLibs.$prefixId = EXT:<directory_of_plugin>/pi/class.$prefixId.php
should be:
    includeLibs.$prefixId = 
EXT:<directory_of_plugin>/pi*1*/class.$prefixId.php
Sorry about that, I was doing 25 things at the same time!!
Thanks!!
Joshua Preston.