Printing problems

Hi all 3D printer fanatics out there!

I have a problem I can't figure out whats wrong. Maybe some one out there have a clue what the issue can be!

I have drawn a detail in 123D design. Exported it as sal with the settings "fine". Imported in Simplify3D and tried to print it out. After approx. 7 mm of printing hight there seems to be a week layer and i can't figure out why. I tried to print a similar detail 2 weeks ago and that part shows exactly the same symptom. I have a Vertex 8402 3D printer and run this project with black ABS with a temperature about 230 degrees at a speed of 2400 mm/min.

Take a look att the images and see if you have a clue. i'm most grateful to anyone how can bring some light into my darkness.