When you come to upgrade an existing implementation of Sage CRM v7.1 to Sage CRM 7.2 you will need to check code that references to the GetCustomEntityTopFrame() method
This is likely to include code for both 'Hand cranked' custom entities and those entities built using the Advanced Customization Wizard for Sage CRM v7.1.
The .NET API method Web.AddTopContent() uses a different way of referencing the TopContent area of the screens and I expect there to be very little issue for custom assemblies.
Hiding from Forward/Back buttons
Another area you should to check in the use you have made to ASP pages that were hidden in Sage CRM v7.1 from the 'forward' and 'back' buttons. This alteration is likely to have been made in a custom include file (eware.js, accpaccrmnolang.js, sagecrmnolang.js).
eMsg = CRM.Init(
In the above code the 5th parameter on the CRM.Init() method set to 'true' indicates the page is hidden from the Sage CRM v7.1 history.