That message means that there is an unresolved symbol in the CommandBase class. The weird name for the symbol: "_ZN11CommandBase6pickUpE" is because there can be many symbols that have the same name (for example overloaded methods) and the compiler generates "mangled" names. This allows them to be different from one another even though they have the same name.
In CommandBase you usually list static pointers to all your subsystems, then include the "CommandBase.h" file in each command. This makes it possible for the commands to call methods on the subsystems.
Perhaps you referred to a class in CommandBase called pickUp that wasn't defined there. If you use RobotBuilder, it automatically generates that file for you, but if you write the code by hand, you need to remember to add each subsystem to CommandBase. You can see more details if you look at the WPILib Cookbook which is located here:
http://firstforge.wpi.edu/sf/go/doc1297?nav=1
In any case, you seem to have it working now.
Brad