I know this is an old thread but in my search for a solution for the same problem, I eventually found a solution that no one else seemed to mention so thought I have to post it somewhere in a hope it will help others.
After 2 days of being unsuccessful with the Arduino Software and even with 'XLoader' trying all the recommended steps of reloading software, resetting the Rumba board etc, I had to start thinking outside of the box.
I was positive that I had the correct Board selected and the correct port. I had also loaded the correct USB RUMBA software.
After giving up with the Arduino program, consistently getting the 'Time out" message I then tried with the free program "XLoader" but even here the RUMBA board would sit with the RX flashing every 10 seconds or so and after a very long wait I found that the program had hung up. After rebooting the computer and the board, it got me thinking for other solutions that had not been posted yet.
The answer that worked for me was the following. (Sorry this is a Windows 7 solution but I am sure it will help with other OS's as well.)
Windows - Go to 'Start Menu'
Go to 'Device Manager'
Select the port that is your Arduino/Rumba board (in my case it was Com 8)
Right click on the port and select "Properties"
select the 'Port Settings' tab
change 'Flow Control' from none to "Hardware"
After making the change and reloading XLoader, suddenly all the TX and RX lights on the RUMBA board lit up like November 5th. Oh Joy.
I then went back to the Arduino Program and tested this and it worked as well.
So it seems that the port is trying to do basic flow control hand shaking and this is why the Arduino software eventually times out giving the errors as posted by other contributors to this forum.
The clue that helped me reach this conclusion is that with the 'XLoader' program running, I noted that the RX led on the RUMBA would flash every 10 seconds or so which made me suspect that the board was waiting for something. I can vaguely remember things about 'Clear To Send' and 'Request To Send' from back when using old dial up modems to connect to the world.
I really hope this helps someone else. If it does, please post back here to let others know that it worked.