First up, what's an "encrypted one". Do you mean RDS using encrypted disk? Or do you mean requiring SSL connections? Did it used to work, in the same network?

A few things to check:

• Did you tick the "allow public access" tick box when you created the instance?
• Are your security group and routing rules set up correctly? NACLs?

This isn't a full answer, but it's too long for a comment. If you can edit your question to include a lot more detail we might be able to help.

First up, what's an "encrypted one". Do you mean RDS using encrypted disk? Or do you mean requiring SSL connections? Did it used to work, in the same network? What exactly have you changed since it last worked?

A few things to check:

• Did you tick the "allow public access" tick box when you created the instance?
• Are your security group and routing rules set up correctly? NACLs?

This isn't a full answer, but it's too long for a comment. If you can edit your question to include a lot more detail we might be able to help. Screenshots of your RDS configuration, routing, and security groups might help if you think any of them are relevant.

I have a basic tutorial on setting up RDS here.