Hi
the problem is due to your server memory, either you restart the server or follow Srinivas, or Sunny's, recommendations. Both are same..
you have to make sure your server memory should come down.
we had similar issue and found our server memory was almost full. and we restarted the server and the upgrade process continues without problems.
so make sure your server memory is not full.
you can see below example of a server showing full memory utilized...and the shadow instance
was not starting. we have restarted the server and all went well.
I am just adding this info for future reference for our community.
Regards
Ravi