I've never seen the "System In Use ..." message issue first hand, but I will see occasional "Command failed" messages, usually if I start sending commands too soon after downloading a program to the TSU. With respect to the "System In Use ..." message, I'm beginning to wonder if there is an input buffer overflow issue in the RFX and the error message is misleading. If there truly is another user working with the RFX, then "System In Use ..." is the correct response.

Consider the possibility that, when the RFX is being hit with several commands, typical of a volume Up or Down, that commands are backing up in the input queue. I have no idea how long this Queue might be (or if it exists), only that there is a possibility that the next command is sent by the TSU, before the RFX is fully finished with processing the previous command(s). While "Busy" would be a more appropriate response, "System In Use ..." may be the only available response. In fact there may not be any RFX input buffer and the TSU is designed to wait a fixed or calculated interval before sending the next command.

Waiting a fixed or calculated interval could work most of the time, but if there is some sort of garbage collection activity in the RFX, I can imagine that this activity could intermittently upset the timing and cause an overrun.

As a diagnostic, logging the number of commands sent and the times of these events might help establish some sort of pattern.

A work around might be as simple as adding a very short delay between all commands or only when sending bursts of commands, such as a string of volume commands.