If you create another add array, it should look like this:
That is the normal input pin for the array, currently yours is:
Which is attempting to feed information back to your cast to node, but that isn’t actually doing anything and could be causing the error you are seeing. If you switch the add array to an add array node that does not have the pass by reference, it should work. If you did not intentionally have the PBR, this may have altered during conversion, which might explain why you are now getting errors. During testing, we tried this:
This produced no errors.