A : While upgrading your OpenX “openXInvocationTags.zip” plugin missed from your installation .
You can check this one by switch to administrator then click on plugin ,there you can check whether that plugin
was installed or not that plugin(openXInvocationTags).

If it was not installed ,then you can manually install that plugin by browse that file from location
“in youropenx/etc/plugins/openXInvocationTags.zip” then click on install button.

If that plugin was already installed, then clear the cache files from “var/cache/” folder  also
“var/template_compiled/” folder.this should be fixed your issue.