First question is what you're trying to do when the message occurs? Upload?
If so, did you select the correct board and the correct port in the IDE's tools menu?
Which OS are you using and which version of the IDE?
Which board are you using? Clone or original? For a clone, you might have a board with a CH340 chip and under windows (and maybe other OSes as well), you will need the CH340 driver.
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Useful links:
https://www.arduino.cc/en/Guide/Troubleshooting#upload
http://forum.arduino.cc/index.php?topic=73748.0