Does Errand Rider add a resource to another hero's resource pool or simply move it there? If I am prevented from gaining resources via card effects, does Errand Rider's ability help me get around that by moving a resource to a hero that needs one?

It is indeed a move - so if you're prevented from gaining new resources you could still move them around using the Errand rider.

would this trigger the harbor master's response?

would this trigger the harbor master's response?

Apparently there is an official ruling: no. http://boardgamegeek.com/thread/1044315/harbor-master-and-errand-rider

would this trigger the harbor master's response?

Apparently there is an official ruling: no. http://boardgamegeek.com/thread/1044315/harbor-master-and-errand-rider

As an aside, the thread linked here says that Bifur would also work like errand rider - but this isn't true. Errand rider explicitly says move one resource from one hero to another.

Bifur is pay 1 resource on hero X, then add one resource to Bifur. Making it a resource gain effect.