I'm working on an ethernet program. I'm using Windows 7 and Arduino 1.0.1. Hardware is a Mega 2560 and an official ethernet shield. After going through a random(<10) number of iterations the downloading hangs. Usually when it does the message area says downloading and the download symbol is orange but the rx/tx lights don't blink. Closing the IDE and re-starting gives error comX in use. The only way out is to reboot the computer, which is very time consuming. Is this normal?
As I read this it appears the problem is that the "reset" of the Mega is not starting the code upload after the compile is completed.
I had a similar problem with a Mega2560 and Ethernet shield when the hardware was powered ONLY from the usb connection. I used a plug pack to supply power to the Mega and the problem was solved. The resets and uploads are then reliable.