I’m using an Arduino UNO with Arduino software v1.0 running under Windows XP SP3. I have gotten this same error with two different boards, on 3 different computers. When I first connect the board with USB cable, everything works fine for a little while. But after I try to upload my program to the UNO about the 3rd or fourth time, I get an error message “Serial Port ‘COM3’ already in use. Try quitting any programs that may be using it”.
I’ve tried the trouble-shooting hints - like re-assigning the COM port to a different port. Didn’t help. Sometimes exiting the program, unplugging the board, or re-booting and starting all over gets me re-connected - but not always. And the error comes back soon.
Any ideas? This is becoming very frustrating!