DXTBMP will not save changeing File in correct Colours

I have reinstalled my Windows 7 and have since then problems with the DXTBMP. With Paint as Editor i can save the paint files and save as dds. But when I use Gimp 2.8 or 2.9 as an editor, he either does not save the files or he plays them with completely different colors. However, the norm.bmp will be displayed in the DXTBMP after saving in the editor message after reload. But I find no attitude where something could change. Similarly, when saving basically no longer asked for the admin rights. What could be the mistake? New installation did not help.

A300_fuselage_master passanger.jpg 1.png
The first attempt this morning looked very good with the 24 bit. Later I'll try it with the Texture Folder. I think I have luck. , Thanks a lot