Error Message When trying to Upload Code (But only sometimes)

Hello everyone:

I just upgraded to the Mega 2560 for a project I'm working on. I keep getting the following message when I try to upload code: avrdude: stk500v2_getsync(): can't communicate with device: resp=0x01

It was working fine earlier, but suddenly it began giving me this message. Earlier while it was working, I kept having to unplug and replug the usb because it kept telling me that "the com port is already in use" or that it couldn't find that com port, even though I had literally just uploaded stuff to the board. Any suggestions? Also, I'm using Windows 7.

is your program flooding a bunch o stuff to the serial port?