Cause
This error occurs if you attempt to subclass a form that resides in a superschema when the current schema defines additional locales over and above those defined in the superschema. This cannot be supported, as JADE attempts to generate copies of the form for each locale in the current schema but is unable to find copies of the superschema form for some locales.
In summary, in order to subclass a superschema form, the set of locales supported by the current schema must be identical to those supported by the superschema.
Action
Remove the invalid subclass. Alternatively, you can add locales to the superschema or remove locales from the current schema until the two sets of locales are identical.