OK_Tech White Screen

Hi

I've installed the Ok tech web service.  I added the local folder to my Moodle root and then added the oktech folder and wspp folder as per the instructions.  It appears to have installed correctly after notification, but when I click on

Site Administrator/Plugins/Web Services/Api Documentation

http://myMoodleInstallation/admin/webservice/documentation.php

I get a blank white page.  I get the same when I try and add functions to a custom service.

Any ideas

Andy