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Is this the first time you have plugged in your phone to the computer?
If not, try to reinstall the drivers.
Or, uninstall, then reinstall the drivers.
What computer OS do you have?

Have you rebooted the computer after the uninstall/reinstall of the drivers?
Try using the factory usb cord and disable/enable usb debugging
Can you explain that pls ;D
Can you explain that pls ;D
Have you tried a different cord?
Yep I tried using the factory cord (the white one) , but same results ...
The problem is probably with the PC as when I plug the phone in the USB it doesn't install the software correctly but instead it shows that error msg
I had a similar problem at one point. I either updated the drivers or changed ports/cord and it went away. The galaxy note toolkit indicated that it was connected in any case.

Where did you download the drivers from?
Download directly from Samsung
I went there but I couldn't find it ...
But whats the difference anyway?