Could not upgrade to version X
If you get a message like,
“Could not upgrade to version 1.5.7. We detect that you currently have v1.5.5, and must perform the updates to get to version 1.5.6 first.”
What has happened is that the upgrade has stopped because one of the tests which ensures prior updates were done has failed. Each database upgrade to version X will spot check whether all prior upgrades have been completed, and stop if not.
zc_install/includes/systemChecks.yml contains the list of checks done at each version to ensure that the database has actually been up to date. So in the case above, reviewing the 1.5.6 checks will narrow down the things to check to see what might have failed.
One very common root cause for this issue is a failure running an
ALTER TABLE required by an upgrade because the table in question still has old format dates. See the page date standardization for instructions on how to fix this.