OJS Server Troubleshooting

I need help fixing existing issues on my OJS server. I've been encountering error messages and user access problems. These issues started within the last week and need urgent attention.

Key tasks include:
- Diagnose and resolve error messages
- Fix user access problems

Ideal skills and experience:
- Experience with Open Journal Systems (OJS)
- Strong troubleshooting skills
- Familiarity with server maintenance and security

Please provide your experience and approach to these issues.