1.3.9h to 1.5.1 error on updating database

I am busy installing 1.5.1 in admin_new. I made a backup of my DB as suggested and used ZC-Install to upgrade the DB

I got the follow 4 errors

SKIPPED: Cannot drop index page_accessed on table admin_activity_log because it does not exist.
SKIPPED: Cannot drop index access_date on table admin_activity_log because it does not exist.
SKIPPED: Cannot add index idx_page_accessed_zen to table admin_activity_log because it already exists.
SKIPPED: Cannot add index idx_access_date_zen to table admin_activity_log because it already exists.

Is this something I have to be concerned about?

nope. Hard to drop something that doesn't exist or add something that already does.:P

So was it something that had not been installed on a previous update?

Is it something that is supposed to be there or can I just ignore it?

In this case those specific messages can be ignored.

Thank You