Hmm at a glance it looks like you’re connecting the Family Type rather than the family instance, while trying to associate instance parameters, but I’m not certain if that is the issue. Do you mind sharing your RFA files?
@Fiesta ah yes it was as I thought, you needed to be connecting the family instance to the Python script, not Element.ElementType. My example in the original post was using Element.ElementType because I was associating Type parameters. Regardless, the script has been revised after another user modified it to accept lists of elements, which revealed a potential for mismatching of the parameter lists. So included in the .dyn attached is the new and improved version of the Python script, which can also be found here: Associate family parameter in a family