I have no experience with MAK, but from reading the doc at Converting KMS Clients to MAK Activation, it seems to me that you have perhaps installed the MAK key on the reference computer by simply entering it via Control Panel -> System -> Change your product key.
According to the doc, the client will then activate itself over the Internet one time. If you have then taken the image and transplanted it on another computer, then in effect you have transplanted an activated system into different hardware, therefore requiring a second activation.
The simplest possibility might be to enter the MAK key on an unactivated reference computer while it is disconnected from the Internet. In that case when the image is installed, it will activate itself once connected to the Internet.
Another solution might be to activate the reference computer using the second method :
slmgr.vbs /ipk <MultipleActivationKey>
The MAK client then does not try to activate itself automatically, so you can then take an unactivated image. Hopefully, after installation the image will activate itself sometimes later, but the documentation doesn't specify when and if, so a little doubt still remains whether the activation will have to be done manually.