The “Database table is locked” message is just a warning and Grafana automatically retries. This is a limitation of using Sqlite as the backend db. If you have lots of people saving dashboards then this could be a problem but then you will see errors and not just the warning. So this has nothing to do with your problem.
A 502 error means that the connection between Grafana and Graphite does not work.
- Does the graphite url work? Can you access http://10.10.2.229:8080 from your machine and from the server? (you should come to the graphite browser page)
- You can try adding the port in the Windows firewall. This is an old video but I think it is mostly the same procedure: https://www.youtube.com/watch?v=cli-Rke3KYo