How do you get Redis connections working within an Amazon VPC private subnet?

I have an Amazon VPC setup with a private subnet containing 2 instances. One of them has redis running on it, the other instance I want to use to connect to the redis server. I have the redis instance listening on port 6123. When I connect locally on the Redis instance, everything works, but when I try to connect from the other instance on the subnet I get:

Connection refused - Unable to connect to Redis

I setup two separate VPC security groups, one for the redis server, allowing inbound connections on port 6123 using the other instance's security group as the source. Likewise, I added a rule to the security group for the other instance to allow outbound traffic on port 6123 to the redis-instance (using the redis instance's security group as the destination).

Is there something I'm forgetting here? Another rule that I have to add? Or a special route I have to setup?

Thanks for any help/direction, Tom