Let me say at the outset that I am very new to Dynamics AX role centers and analysis services and really have a lot to learn. However I thought I would share the following problem with setting up role centers and the associated solution that I found.
Problem description: After installing role centers on AX2012 RTM CU 3 with SQL Server 2012 the following error is displayed “An attempt has been made to use a data extension ‘AXADOMD’ that is either not registered for this report server or is not supported in this edition of Reporting Services. (rsDataExtensionNotFound)”

The Event log on the SSRS machine says the following: Role Centers / Analysis Services: Report Server (AX) cannot load the AXADOMD extension.
Problem resolution / investigation: After chasing my tail on this one for quite a while (including multiple re-installation etc) trying to figure out why the “AXADOMD” SSRS datasource extension was not installed I discovered that the problem did not lie with “AXADOMD” being missing but rather it might be having issues when it was loading.
Looking at the SSRS log files (C:\Program Files\Microsoft SQL Server\MSRS11.AX\Reporting Services\LogFiles) I discovered the following message:
ERROR: Exception caught instantiating AXADOMD report server extension: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. —> System.IO.FileNotFoundException: Could not load file or assembly ‘Microsoft.AnalysisServices.AdomdClient, Version=10.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91’ or one of its dependencies. The system cannot find the file specified.
File name: ‘Microsoft.AnalysisServices.AdomdClient, Version=10.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91’
at Microsoft.Dynamics.Framework.Reports.AxAdomdConnection..ctor()
This lead me to think something might be wrong with the Microsoft.AnalysisServices.AdomdClient itself despite the AX installation validation showing up that it was installed already.
Paying a quick visit to C:\Windows\Assembly revealed that only AdomdClient version 11.0.0.0 was installed

The simple solution to this issue was to install the 10.0.0.0 client from http://www.microsoft.com/en-za/download/details.aspx?id=23089 after which SSRS no longer complained.

I hope this saves somebody some of the hassle and time that I have spent on figuring this one out.