Yesterday I upgraded owncloud to Version 8.1.1-7 from SynoCommunity on my Synology NAS. After upgrading the webinterface only showed me this:
Today I decided to backup the database and reinstall, and then replace the database with the existing one. I found out, that in my case the solution was really simple – the prior owncloud version prefixed all tables with „oc_“ by default, but the newly installed package did not do this. The solution was to rename all tables from the old version and remove the „oc_“ prefix. Et voila – owncloud started upgrading my database and worked like a charm.