Hi Robear,
in the meantime I have found the process that was responsible for the trustedinstaller activities. It was the xenservice.exe that was installed together with the Citrix XenCenter on my machine. I have killed this process and suddenly the trustedinstaller.exe stopped its activities. So the problem is solved now because the XenCenter can work without this process and I will remove it from the auto
Thanks for your help.
Martin