Error rebuilding file /var/www/...: Publish error in template '...': Error in tag: error in module...: Publish error in template '...': Error in tag: Error in tag: error in module ...: Publish error in template '...': Unknown tag found: ...
The weird thing was that the error only happened when publishing the particular file via the publish queue using the 'run-periodic-tasks' script, but it didn't happen when publishing the file 'by hand'.