Go to your Apple Menu/Control Panels/Extensions Manager. Locate the SequelGammaPlus extension and make sure that it is active (there should be an X in the box to the left of it). If you have a Wacom drawing tablet driver, disable it by unchecking the box to the left of the extension name. Restart your machine. Once you have successfully built your monitor profile, you can enable your extensions and restart your machine.
Connect your colorimeter directly (not through a hub!) to an available USB port on your machine. Ensure that the port works with other USB devices. If you do not have a port available, temporarily disconnect another device and plug the colorimeter into that port. Restart MonacoEZcolor and try to build a monitor profile using the colorimeter. After creating your profile, disconnect the colorimeter and reconnect your other device.