Serial Port Problems

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!

At one time xp would assign a new comport number to USB to serial adapters each time the adapter was plugged in. xp would then say the previous assigned comport was already in service the next time the adapter was plugged in. The fix for me was to go into the advanced comport settings in device manager and assign a com port to the adapter. If xp said com port 8 was already in service and I had nothing using com port 8, then I would assign comport 8 to the adapter. xp would say 8 was already in use by another device, but i would go ahead and assign 8 to the adapter. After that xp would always use com port 8 for that adapter with no further issues. The UNO does not use the FTDI chip, so the UNO serial driver maybe somewhat foreign to xp.