When you say Arducopter 2.6 I will assume you mean an APM 2.6.
Be sure you have loaded firmware version 3.2.1 which is the last compatible version for APM hardware.
Use the "Initial Setup/Mandatory Items/Compass" screen so you don't have to keep working through the wizard.
Make sure you have NO magnetic interference around you, no power cables overhead or under ground, water pipes will do it too, away from tin sheds, etc.
In the Manual calibration screen turn off "Auto complete".
If you get failed attempts quit Mission Planner and restart it.
Hope that helps.