At the moment, at least on One To Many associations, Woko uses the private field declaration in order to find the compound type of the association.
The problem is that the property name is used to lookup the attribute, and they can have different names (getXxx() vs private yyy).
This is very clear here :
net.sf.woko.actions.ChangeOneToManyActionBean#getCompoundType
Also, there is a typo in the error message :)