Focusrite Scarlett 2i2 input problem

i ve just got this sound card plugged in my Mac book pro end 2011 and i have no signal when i play guitar. When i record i’ve got an error message about desynchronisation, but it is in French, like there is concurency on an output device.
I’m new on Mac and audacity and i don’t know how to fix it.
Thanks for the help…
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solved! The scarlett is stereo and my input was mono but not the right side. !!! :smiley: