Enable NAT-PMP or UPnP for iCloud.com

I'm a Mac user with a Netgear 3500L v2 and Tomato Version 1.28 by shibby installed.

Using www.icloud.com backup for mac also have a future called "Back to my Mac". When I try to activate it I get he error message that I have o turn on NAT-PMP or UPnP in my router for this to work.

Finding this options in the router under Advanced I check the boxes to enable. But then I get "NAT-PMP or UPnP must be enabled in least one LAN bridge"

I have no forwarded ports in the list above.

What do I need to do here?

Thanks!