Trying to upgrade the Data Store (Portal & Server just upgraded), but get this error:
Then when I try to start the PublishingTools I get this:
Do your ArcGIS Server logs provide any useful information from around the same time you attempt to start the PublishingTools service?
This support documentation might be helpful, although it's regarding an undefined error in a slightly different context.
Did you use Enterprise Builder, per chance?
Had a similar error when using AEB to upgrade from 11.3 to 11.4. Checked the install versus another machine and turned out not all new files where copied to the installation directories (about a third were simply missing). Really weird; the install process was happy otherwise, but the post-upgrade couldn't proceed since the components weren't running correctly (including the publishing tool service).
A simple 'Repair' via the Control Panel -> Programs fixed it. The missing files were back and Server ran correctly again.