The iPad should be connected to the left USB port, and the laptop to the right USB port. Refer to the image below, and use the following settings:

iPad / Lemur
MIDI Target 0
Input: iCM USB D2
Output: iCM USB D2

Computer / Ableton Live
Control Surface: LiveControl 2 0
Input: iCM USB D1
Output: iCM USB D1
Track Input: iCM USB D1
Sync Output: iCM USB D1