With my newly assembled Ultimaker, and Netfabb software I have exactly the same experience.
The advice given, also in this forum, is to generate the G-code with Netfabb, and send it to the Ultimaker with ReplicatorG.
If I perform these steps I see the G-code being created and imported in ReplicatorG, however, when making the object on the Ultimaker it firsts pauses an estimated 10 seconds, then directs the print head to the maximum Y position and stops there.
Does anyone have a clue how to execute this process properly?
