Thanks a lot!
BUG:
The problem is a bug in adobe premiere!
The Problem is, that in germany decimal numbers written like this: 3,1416 (with comma) instead of 3.1416 (dot).
The projects XML file use the "," to separate numbers. So the values 1, 2.5 and 3 will be saves as: 1,2,5,3. An that seems to be the problem.
I changed the windows settings for number layout and it works. Adobe uses the windows number layout settings. That's really crazy!
EXAMPLE:
0.36015... must be 0,36015...
0,166666... must be 0.166666...
WORKAROUND UNTIL BUGFIX:
I changed my windows number settings. So I can re-open saved project files.
Of course it doesn't help to open corrupted project files.
FIXING:
It's not easy to fix damaged files. My project XML file contains over 2000 Keyframe tags, an each of them contains 6-50 values, could be corrupt. In my case there are round about 5000-10000 corrupted values. To fix it manually... oh nooo... it would be easier to create a new project :/. Perhaps I try to create a little application to auto-fix my corrupted files. I hope it will be possible.
Helpful was this link: https://forums.adobe.com/message/4155936