Loosing sprite association when transferring prefab

Hey, it is me again (GlobalGameJam forces me here today) We are currently trying to transfer some of the prefabs we build from one machine to another. A prefab in this case is a main object with some children. When exported into a package we are able to keep the script associations intakt, while the childen (which are Sprites) loose the connection to the texture (It states 'missing' after loading on another machine) We tried the normal way, exporting into a package, building the main object from prefabs itself. but in every case the script<->texture association is lost.

Any way to prevent this? Thank you all for your consideration in advance ;)