"com7 already in use" problem

I was working with my Arduino Mega (new version) when suddenly I could no longer upload programs to the board. The error message was "Com 7 already in use"

This problem seemed to occur after I installed two programs on my computer: LabView and Procomm. I'm not exactly sure if I was able to program the Arduino after these programs were installed. In any case I uninstalled both programs and got the same error.

I tried reinstalling the USB driver and got the same error. I tried a second mega and got the same error. I tried a Duemilanove and got the same error (after changing the board and serial port settings). I tried a different USB cable and got the same error. I tried a completely different computer and got the same error.

Any insights would be much appreciated.


I've managed to solve the "com7 not available" problem.

I think that my program was uploading to the board, its just that I was using the Serial functions incorrectly. I hypothesize that if a Serial function is used incorrectly there is some sort of interaction between the Arduino and the Arduino IDE that causes the lock-up of the com port. In my case I was writing a program to use serial port 1 on the Arduino Mega. I invoked the following function: Serial1.println( ); The Arduino reference does not state that this function is compatible with serial ports other than the standard port 0 found on all boards. So I presume this command can't be used, it was an error and caused the lockup. I also got the same behavior when I invoked Serial.write( ); instead of Serial1.write( ); Not a syntax error but a program error because I did not initialize serial port 0.

When the "com 7 not available" problem occurred I managed to regain control by closing the Arduino IDE, pulling the USB cable out of the board and power cycling the external power supply I was using to power circuits connected to the board. I could then reconnect the board, open the Arduino IDE and I got my serial port back in action (most of the time).

Hope this help people with similar problems.