Why am I getting a serial port error when Compiling and Downloading? | FAQ (Frequently Asked Questions) | Forum

If you have the Serial Monitor open while downloading, you may get a serial port error because the Serial Monitor is still accessing the serial port.  This will be resolved in a future version (after 1.0.0.18).  For now, try closing the Serial Monitor before downloading to your target.  If that is not the issue, make sure no other programs are currently accessing the serial port.