Cross-Pod mapping with Smartlist

Summary:

I'm trying to do a cross-pod map from a Planning application to a FreeForm application. Several dimensions are using smartlist to dimension mapping. I've cleared up several real errors due to members not existing on both sides the same, but now it's down to an error message that gives no real information:

Push Data failed. Error: The following member(s) [null] are not available in the target. Map them to valid member(s) in the target or exclude all available instances in the selection including in any alternate hierarchy.

Is it even allowed to do smartlist to dimension mapping when using cross-pod? I did set my options to prioritize smartlist entry names.