Device will not join in Profile Manager

Forgive me, as I could be being very silly. But really would appreciate some help here.

I am attempting after installing Mavericks Server to join a device (iMac intel, running OSX Mavericks) via profile manager.

Everytime I go to myserver/mydevices on the iMac I install the trust profile and then I click the blue Enroll button. However, this is where the issue arises. The device will only appear in Profile Manager as a Placeholder - it will pick up the name of the iMac and it's serial number, but it will only be a placeholder not a fully managed device (I do not get the options in myserver/mydevices to wipe or lock etc. and the device will not appear in there). I am logging into the local admin account of the iMac - and have also tried it as a network account. STILL don't work.

Could anyone shed some light on what the issue could be here?

The host machine will join fine (I did this as a test).

Thanks in anticipation! This is a niggly issue which is driving me MAD!