I've just started getting these with some of my models and don't really know why.
I just added a polymorphic relation to one model, could that be a culprit?
OS X 10.8.2
I got the same error message with 'embeds_many' in the model.
Hi, my issue is about embeds_many problem but could also contain a workaround for you:
Merging into #1552.