Curently to activate license for monotouch per IMAC, you have to install later version of Xamarin which probably will come with Xamarin.IOS Framework that your existing IOS application is not supported Posted by Unknown , Monday, September 9, 2013 at 7:01 AM, in

Curently to activate license for monotouch per IMAC, you have to install later version of Xamarin which probably will come with Xamarin.IOS Framework that your existing IOS application is not supported.
So how to activate license for monotuch per IMAC without having to install Xamarin.

Here is the work around (so-called Offline Activation http://docs.xamarin.com/guides/ios/getting_started/installation/offline_activation):

1- Install Xamrin and activate the IMAC
2-   Go to Finder and Hold down Ctrl Key on Go Menu in Finder and you will see Library
3-  Click on Library and go to Library\Monotouch\ And back up License.v2
4- Erase HD, Redownload Lion OS, Re-install, and Clone Co-worker’s HD using Migration/Assistance tool so that you do not have to re-install
all the applications again
(tip: http://www.youtube.com/watch?v=OtUw-vo606w)
- Then past the back up of License.v2 under Library\Monotouch\ and It compliles successfully now.
There you go! try to compile your project now.

Remark of the issues that leads to the solution above:
- If we do not activate the monotouch per IMAC we will get error - mtouch exited with code 98
that means you have not activated your monotouch on your MAC system.
http://www.gregoryvarghese.com/index.php/mtouch-exited-with-code-98/
- If you add reference to dll Microsoft.Synchronization.Data.dll in your project mainly for client/server database Synchronization:
after you install later version of Xamarin to activate your IMAC you might get errors  "is marked as an override but no suitable method found to override" on Methdo ApplyChange(...) which is an abstract method
on Base class ClientSynProvider
public abstract SyncContext ApplyChanges (
SyncGroupMetadata groupMetadata,
DataSet dataSet,
SyncSession syncSession
)

Following the solution I have mentioned got rid of these issues.