Hotfix will be enough for this.
After Update to 2.6.1 - same Problem but not longer the above describe Errormessage.
1000 Games or 10 Games. Sometimes some Games are going to be installed sometimes not. But allways a Timeout after some Minutes.
I found the Problem now. The Installer is not stopping on Defect Games like it does if you try to install the Games without the Mass Installer. So it goes into a Timeout.