Nevermind, I spent some time with the various VTD tools..

I solved the problem by using the VTDTool.exe instead of the VTDManager.exe tool..

VTDManager adds the image but cutts off a pixel on both the right side and bottom of the image. Resulting in a texture of 256x256 (so it says) but in reality it only imported 255x255 and decides to make a black line for the last pixels...

yeah bad english, soz