Also, the 7mm head set screw on the right side between the two tension arms needs to be backed out quite a way for the unit to come out.Judging from the picture you attached I assume you followed the Article for removal of the headunit?
Are you certain you managed to get all the four aluminium arms to release the unit? At which point is the unit stuck? Half-way out? An inch? Not at all? Since the pic you attached isn't of your headunit it is hard to tell how far you got. If you didn't get it out at all my bet would be that one or more of the arms aren't under enough tension to actually release the headunit.