Do you mean OJS 3.4.0-6 (OJS 4.3.6 doesn’t exist)? Have you checked your PHP error logs. If you could do that and report back on error messages found there, that will help identify the issue. In instances where you see errors like this, the information displayed on the browser is often not sufficient to be able to identify the problem. If you’re unsure about how to find your PHP error log, please see here: How do I find my PHP error log?
-Roger
PKP Team