You should do the following:
1. Disconnect your note 10.1 from PC and close odin
2. Go into download mode (make sure to not forget to press the volume up button to enter download mode (yes, happened to me ...))
3. Connect your note 10.1 with your PC
4. See if your PC recognizes your note 10.1 (watch usb icon)
You should be connected to the internet, because windows may install some drivers here.
Wait until those drivers finish installation.
5. After installation of those drivers open odin
6 Hopefully odin now recognize your note 10.1
I hope that helped...