[NTG-context] Going crazy with font conversion (diaeresis)!

Hi, using HelveticaNeue (came with OSX) was fine. But using Helvetica (from OSX system fonts) just won't work: - when I have converted the .dfont to .pfb with FontLab the diaeresis of the german Umlaute (äöü) are too far to the right. - when I have converted the .dfont to .pfb with FontForge the diaeresis of the german Umlaute (äöü) are OK, but all other elements like Macron, Cedilla or Ogonek are too far to the left (!). Anybody knows this strange behaviour? And even better what to do to avoid this mess?? Steffen