Starting from 1/1/2003, or Cocoon releases > 2.1.2, the following change is required to all your form definition files.
In the form definition, for widgets that have child widgets, those child widgets should now be embedded inside a wd:widgets element.
Here's what practically needs to be done:
A form definition that previously looked like this:
<wd:form> <wd:field .../> <wd:field .../> <wd:repeater .../> </wd:form>
should now become:
<wd:form> <wd:widgets> <wd:field .../> <wd:field .../> <wd:repeater .../> </wd:widgets> </wd:form>
The same is true for the repeater widget:
<wd:repeater> <wd:field .../> <wd:field .../> </wd:repeater>
becomes
<wd:repeater> <wd:widgets> <wd:field .../> <wd:field .../> <wd:widgets> </wd:repeater>
The aggregatefield widget had already a container tag, but it was called wd:children. It should now be renamed to wd:widgets.