Since no answer can be found on this topic,
my situation was corrected this way:
This issue is happening because of a wrong SUM version
for the target release a higher version of SUM needs to be used.
For that you reset the upgrade as it is mentioned in the SUM guide
and start the upgrade using the latest SUM version available on
http://service.sap.com/swdc
Additional Components -> Upgrade Tools-> SL TOOLSET-> SL TOOLSET
1.0->
Entry by Component-> Software Update Manager (SUM)
You
could also have a look to its central note.
1878193 - Central Note -
Software Update Manager 1.0 SP10
Regards,
Roger