Import Dataport problem

I have a weird problem. I created an import dataport to import Segment Lines. There are no 'GUID' or 'BLOB' fields involved. The file has multiple records. I make sure that line numbers are increased properly. But for some reason it just stops after the first record being read. I'm using NAV 2009 SP1 (Classic). The dataport DataItem is an Integer and no filters used, and all fields defined as dataport fields are matching the data file Also no issues with option fields etcetera... It just creates the first record correctly, all fields are matching but then it stops. The debugger doesn't give me any hints either. And no errors during the import run.
Also: I checked the import file. Everything is correct. CR's are defined after each line.

Anyone any suggestions?

Thanks!