Yes. I think I can see the issue. RUT900 doesn't load the necessary IPsec firewall rules. Can you try restarting the firewall of RUT900? You would have to login via CLI (username: root; password: your router's password) and execute this command:
/etc/init.d/firewall restart
Can you try this and tell me if it worked? If you're having trouble with CLI, instructions can be found here.