Help: multiple route question

I have MT Router OS v3.23 with simple queues set up for my system connected to a T1. I am adding bandwidth from another location. I have a RB450 in a remote location with the other connection. I have the ip addresses set on the RB450 and from what I have read, all I should have to do is to put the IP address of the other “gateway” (RB450) into the IP>Routes and add the gateway IP address to the second line and it should add that one also.
Everytime I add this it pertty much kills the routing, remove the entry and all is fine.

What am I doing wrong to add a second gateway