I did included the c4d_resource.h and the error disappeared.
I was migrating by simply fixing the errors that appeared inside Xcode, until everything was clear.
But now, I started by duplicating a similar plugin from the sdk and pasting just the parts of the code that belong to my plugin.

The "solution" I came up with was this:

	doc=op.GetDocument()
	doc2=c4d.documents.IsolateObjects(doc,[op])
	doc3=doc2.Polygonize(False)

and then go through all the objects of doc2, recursively.
Is this a correct way of doing things?

It seems not to crash now. I made sure I freed all the bitmaps and flushed all containers.