In the past week, I have upgraded my Kunena installation twice on the Master site from 1.5.8 to 1.5.9 and then to 1.5.10 and am getting errors on my slave sites that

"Upgrading Kunena to version 1.5.10 has failed!"

* Your forum may be missing some important fixes and some features may be broken.
* Please try to upgrade again. If you cannot upgrade to Kunena 1.5.10, you can easily downgrade to the latest working version.
* Our support forum can be found from: www.kunena.com

Everything looks like it is running fine, so I'm not going to mess around more, but will the installation finally work on the slave sites?

Has anyone else had this problem?

You just have to go in the slave site and re-install also the Kunena 1.5.10.
So that they will perform the upgrade of the DB layout or data.

Ok... will give that a try.