I still have the same issue as I did months ago. I followed all the advice on this post and others like it that I have found.

People that use both of the 2 TSU9600s are pissed because of "command failed" errors.
I have all the latest versions of firmware on the two TSU9600 units and the RFX9600.
I have strong signal my dedicated WAP set to no security, and using MAC filtering. Network is good and works about 80% of the time.

When I get the "command failed" errors, the busy light on the RFX9600 lights up solidly for 30-45 seconds, during which time no commands can be sent to the base.
Once that clears, all starts working again for 1 minute or 1 hour.
I'm the only one in the house now, no other devices active except for a cordless phone and my laptop. Neighbors too far to worry about.
WiFi analyzer on my Droid doesn't show any other SSIDs in range.

I'm running both DirecTV HR24 receivers thru the serial ports as well as Denon AVR3311CI.

D-link DIR625 is used as a router with it's own SSID and WEP security), but wireless communication for the prontos is handled directly thru WAP.
I tried few different WAPs, always setting them to no security, using MAC filtering only.
TSU9600 is set to:
Wireless Timeout: 24 HRS
Roaming Strategy: Default
SSID: ProntoWAP
Encryption: Off
IP Settings: Fixed IP
IP Address: 192.168.0.160
Subnet Mask: 255.255.255.0
Default Gateway: 192.168.0.1 (also tried 192.168.0.2 WAP IP)
DNS: 0.0.0.0

RFX9600 set to DHCP

Router: 192.168.0.1;
DHCP Range 10-99;
Channel 11
WAP: 192.168.0.2;
Security off, MAC filtering used for Prontos;
Channel: Auto (tried 1 and 5 as well).

Like I said, I can connect, just can't seem to stay connected.
Keep getting 0405 Extender 0 didn't reply