Appropriate policies/rules for internal to internal via nat'd ip

So here's the situation...

We moved from the UTM 9 to the XG firewall recently and have had issues in the way some of our rules/policies worked.

For SnGs, I'll use the 10 network for internal, and the 128 network for internet.

Core switch = 10.0.0.1       Firewall = 10.0.0.2      Public IP Network, GW, Subnet = 128.0.0.128, 128.0.0.129, 255.255.255.240

I'll do my best to illustrate the layout below.  We have a computer (10.0.0.50) on the internal LAN that has some services.  We have an SNAT /w Masquerading and a DNAT business rule that states 10.0.0.50 can send traffic as 128.0.0.141 and recieves internet traffic sent to 128.0.0.141.  This rule works with no issues.

Computer 2, with IP address 10.0.0.51 can talk to 10.0.0.50 and 50 to 51 with no issues.  10.0.0.51 can NOT talk to 128.0.0.141 at all.

How do we allow our internal machines to speak to 128.0.0.141?  We've tried SNAT, DNAT, FullNAT... What are we doing wrong?