After the advice from vice, i did know where to look at.
it was an wrong registry entry.
tried the installer on my third system on the same machine. It runs very smooth.
The wrong registry entry is certainly my fault. had to work a lot with the registry for a project at my university and hadn't time to reset the system. seems like something went wrong unnoticed.
Great Thanks for the help.
Correct my if i am wrong twilly, but you only have to run programs as an administrator to let the programs have access to system directories like the temp directory or the appdata folder. This is what the UAC is blocking. So you can deactivate the uac, which is certainly not a good advice for some people or you can give a program administrator rights. if you right click on the exe, go to the last entry which must be something like properties in english, and go to the compatibility mode, with a checkbox there you can permanently run a program as an administrator. This works for 90% of all programs that i encountered. With that you can have UAC activated and run the trusted programs with whole administrator rights.