Follow up:
The previous mentioned actions did not solved the problem, here below the steps needed in my case:
1/ open admin cmd.exe and type
DISM.exe /Online /Cleanup-image /Restorehealth
(https://support.microsoft.com/en-us/kb/947821?wa=wsignin1.0)
2/ wuauclt.exe /resetauthorization /detectnow
These steps were necessary after the following ones, successful but not solving the issue
– reboot
– sfc /scannow
– rename softwaredistribution folder
– WU agent update to last version (manual KB install)
– Windows update reset (https://support.microsoft.com/en-us/kb/971058)
– wuauclt.exe /resetauthorization /detectnow (without dism first)
Regards
Booster