Problems uploading to Mega 2560

After uploading I am getting the message "avrdude: stk500_getsync(): not in sync: resp=0x00"
What does this mean and what do I do about it? I have been successfully uploading programs to another 2560, but I recently
started using a new one. I successfully uploaded once or twice to the new 2560 before this started happening.

Another troublesome problem I am having when I upload or open the serial link window is a message that "COM4" cannot be found or it is busy. I work around it now by restarting my computer (running Windows XP) and that clears it up for awhile. I am trouble shooting a large program and this has gotten to be a real time burner. Any suggestions would be appreciated.

Thanks,

Barry

I successfully uploaded once or twice

Uploaded what? Can't upload what? With what attached to the Mega?

Any suggestions would be appreciated.

Quit running whatever is grabbing the COM port that the IDE is trying to use to talk to the Arduino. Some bluetooth crap, maybe?

I am using an old Dell laptop pc running Windows XP. It was set up to use a blue tooth mouse through a USB port, but I do not use it. I will uninstall the software for the bluetooth mouse and see if that solves the "COM4" problem.

Does anyone know what the error message I am getting mean? Or where might I find out?

Thanks for the help,

Barry

Do you have "!!!" in your program anywhere? (or has that finally been fixed?)

Oldradio, please check that you have the same baud rate on both sides.
The problem you describe has been discussed in large in the forum, with the conclusion that there is a problem in the IDE 1.0.5.
Some people reported that going back to the older 22 version solved the problem.
Others wrote that only replacing the AVRDUDE.EXE and .CFG from the old to the new version solved that problem.
Please see avrdude: stk500_getsync(): not in sync: resp=0x00 - Troubleshooting - Arduino Forum

I do not use any "!" in my code, so that is not the problem. How do I check that the baud rate is the same in both devices?

One problem solved, but the COM4 problem is still a hassle.
In some mysterious way the Mega 2560 was deselected from the list of models. It is mysterious in that I did not do it. In any event, I reselected the Mega 2560 and all is well on the error message part of my problem.
The COM4 problem is still a mystery. There is nothing running on my PC that could be taking it away. The message being displayed is “COM4” cannot be found. Yet, when I go to device manager and look at the COM ports, it shows Mega 2560 connected to COM4. I have to restart the PC to get it to work again.
I am typically uploading a program to the Arduino, running on a powered controller which employs the Arduino and then unplugging the USB connection to let the controller run on its own. I turn off the controller and when I replug the USB cable to the controller/Arduino I get the “COM4 cannot be found” message when I again try to upload. Maybe the answer is to not unplug the USB connection, but that is not a good solution for me.