Upgrade of an Ironport proxy

From time to time, you may experience failure when upgrading a Cisco Ironport from one version to another. In my case, I had been struggling for days to go from 7.1.0 to 7.1.1.

At the CLI, the upgrade command would fail after a certain random time, claiming a network connectivity issue.  I also have a message popping-up: 

High Latency: (109.905s) for <coro #1 name='<function coro_reader at 0x296995a4>' dead=0 started=1 scheduled=0 at 0x294b7a44>

The solution - in my case - was to disable WCCPv2 on the box and revert to "L4/no device". The upgrade went through like a charm.