Thanks, it was a fine grained policy in ADAC, I had found the settings in the default domain policy but they did not match and after reading your post I checked the ADAC and found the setting.
However, a method of searching all the GPOs to find where one setting is being configured would be useful when trouble shooting a GPO issue rather than running GPResult and then checking the policies to see what has been set, as it can get a bit confusing especially if like me you have just taken over a new network and the GPO labels are not always totally clear to a new admin, I know I have not always understood my own naming convention six moths after setting up the GPO.
Mike