Doesn't seem to be purely a WEP/WPA issue as I've had the problem multiple times tonight using WEP. I am using a fixed channel and a 128 bit key. I'll continue trying different combinations to see if I can find something that works reliably.

These problems all started with the firmware updates for the TSU9600/RFX9600 that added the WPA support. Everything was rock solid before that.

Edit... more info

The problem seems to be limited only to the TSU9600 side of the equation. There is no delay or problems talking to the RFX9600 from the simulator while the remote itself is showing "command failed". I also have some control screens for my home automation that use TCPIP and first use fails on those as well. After the 10 second wait, the "command failed" goes away and communication with my home automation is restored.