Chris Sharp, of Georgia Pines, detected a problem with the upgrade from Evergreen 2.8.4 to 2.9.0. It would fail because of a table being modified while data was being also being inserted into it.
This problem has been corrected and a new release uploaded to the public download server: http://evergreen-ils.org/egdownloads/
If you have already downloaded Evergreen 2.9.0 from that location and plan to upgrade, you must download it again or the upgrade will fail.
If you are planning to upgrade using git, the public repositories have been updated, so doing a git pull will get you the fixed upgrade script.
As the release manager for 2.9, I apologize for any inconvenience this causes.
In my defence, this is the largest upgrade script in Evergreen history so far.