Installing packages using ports after freebsd-update doesn't work on amd64

[Sorin Panca]

Doug Barton wrote:
> Sorin Panca wrote:
>> After upgrading the system using freebsd-update from 6.3-RELEASE to
>> 7.0-RELEASE and after that, from 7.0 to 7.1 trying to install
>> ports-mgmt/portupgrade fails at ruby18 with the following message:
> 
> If you haven't already you have to remove and reinstall _all_ of your
> ports after doing a major version upgrade (6.x -> 7.x).
> 
Prior to starting the upgrade I did a pkg_delete -a. I wanted a clean
system (just like a reinstallation). How do I ensure that all packages
were removed by pkg_delete -a ?
Running pkg_delete -a returns "pkg_delete: no packages installed"

Thank you!
Sorin.