asterisk users - Jan 2011 - Losing registration - ast 1.4.39 and innomedia 6328-2Re

All,

I'm having a problem with an Innomedia 6328-2Re (old Sunrocket Gizmo).  
It keeps losing registration after a period of time ranging from a few 
minutes to a few hours.  It seems that right before it loses 
registration, it fails to send a second register (after the 401 
unauthorized).  Here's a transcript from wireshark (at the end).  The 
last message is all that's received and asterisk now shows
"UNKNOWN" ast
the status:

10676    17:13:05.255123    innomedia    asterisk    SIP    Request: 
REGISTER sip:asterisk
10677    17:13:05.255336    asterisk    innomedia    SIP    Status: 100 
Trying    (0 bindings)
10678    17:13:05.255388    asterisk    innomedia    SIP    Status: 401 
Unauthorized    (0 bindings)
10679    17:13:17.263367    asterisk    innomedia    SIP    Request: 
OPTIONS sip:1015 at innomedia
10680    17:13:17.410876    innomedia    asterisk    SIP    Status: 200 OK

The innomedia is behind a Netgear WGR614v7 router with Comcast as the 
ISP.  But I've already put the innomedia into the DMZ of the router and 
it doesn't appear that it's a NAT issue b/c I can actually telnet into 
the innomedia through the router (DMZ) even after it's lost registration.

It *looks* like the problem is the innomedia since it didn't send 
another register.  But I figured I'd ask to see if anyone here knew what 
the problem could be.  Otherwise my next step is to buy a linksys PAP2T.

Thanks,
Brian