This error could arise if your webapp defines an error page which does not exist. If the configured error page can not be resolved, the webserver tries to display some legacy jsp error page which can fail with this error.
Did you forget to migrate the content of the webapps directory?
See http://developer.axonivy.com/doc/latest/EngineGuideHtml/configuration.html#configuration-errorhandling-customized
Furthermore we've changed that JSTL is in the web-inf/lib dir. But that should not affect you: http://developer.axonivy.com/doc/latest/doc/migrationNotes/MigrationNotesEngine.html#taglib
If these hint hints do not help you. Analyze the log output of the engine - may be this is only a follow up problem which obfuscates the root cause.
