Thank you in advance.

I have a few 2851 Cisco ISR.  This is my NAT Pool config;

    ip nat pool NAT-Pool 38.xxx.xxx.193 38.xxx.xxx.206 prefix-length 28
    ip nat inside source list 1 pool NAT-Pool overload
    ip nat inside source list 100 pool NAT-Pool overload
    ip nat inside source static tcp 172.20.9.3 80 38.xxx.xxx.199 80 extendable
    ip nat inside source static tcp 172.20.9.3 443 38.xxx.xxx.199 443 extendable
    ip nat inside source static tcp 172.20.9.3 3478 38.xxx.xxx.199 3478 extendable
    ip nat inside source static tcp 172.20.9.3 5222 38.xxx.xxx.199 5222 extendable
    ip nat inside source static tcp 172.20.9.3 5349 38.xxx.xxx.199 5349 extendable
    ip nat inside source static udp 172.20.9.3 10000 38.xxx.xxx.199 10000 extendable

Say I want to add another udp port 10001 to the same IP addresses, I get 

> similar static entry (38.xxx.xxx.207 -> 38.xxx.xxx.199) already exists

This is what my interface looks like:

    interface GigabitEthernet0/0
     ip address 172.20.8.1 255.255.252.0
     ip nat inside
     ip virtual-reassembly
     duplex full
     speed 1000
    !
    interface GigabitEthernet0/1
     ip address 38.yyy.zzz.178 255.255.255.248
     ip nat outside
     ip virtual-reassembly
     duplex full
     speed 1000

I am running Layer 3 setup. 

Now I can add the new NAT entry if the router is rebooted and I immediately add it once it is up. 
I originally thought that this was the hardware, however I have all 3 routers with identical configurations doing the same thing.  Note IP assignment are different on each router. 

Thoughts?