I am a biggenner and want to upload sketch on Arduino UNO but its shoing error
i am using win 7 64bit and i've gone through all the steps to troubleshoot described in http://www.arduino.cc/en/Guide/Troubleshooting#upload
Error is following
Arduino: 1.6.4 (Windows 7), Board: "Arduino Uno"
Sketch uses 918 bytes (2%) of program storage space. Maximum is 32,256 bytes.
Global variables use 15 bytes (0%) of dynamic memory, leaving 2,033 bytes for local variables. Maximum is 2,048 bytes.
avrdude: ser_open(): can't open device "\.\COM20": The semaphore timeout period has expired.
Problem uploading to board. See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.
This report would have more information with
"Show verbose output during compilation"
enabled in File > Preferences.