What did you mean by "not opening"?  Please elaborate or show some screenshots.

What are the brand and model of your device?

And the version & build numbers of your MobiControl server?

Sounds like you tried to install android enterprise in a phone that was already past the setup screen (when you first turn the device on or perform a factory reset)

you need to perform a factory reset on the phone.

then when go though the steps it displays. Once you hit "enter a google account" type in "awf#mobicontrol" without the quotes.

it will begin downloading the client (if you have a data connection) 

once it finishes downloading the rest of the phones setup will finish.

open mobicontrol after getting to the main screen on the phone and enter your enrollment ID

NOTE: android+ profiles will not work with android enterprise you will have to create them separately