Problems removing fields from EditProfileForm

[nimeso]

Using _config.yml eg:

Member:
hidden_fields:
- 'Image'
- 'TimeFormat'
- 'DateFormat'
- 'Locale'
- 'LockedOutUntil'
- 'PasswordExpiry'
- 'Salt'
- 'PasswordEncryption'
- 'AutoLoginExpired'
- 'AutoLoginHash'
- 'LastVisited'
- 'NumVisit'
- 'RememberLoginToken'
- 'TempIDExpired'
- 'TempIDHash'

Returns a error when in the CMS Security section... could be a SS issue?
Fatal error: Call to a member function performReadonlyTransformation() on a non-object in D:\wamp\www\mysite\framework\forms\FieldList.php on line 532