Yesterday When I tried to Install the Reporting Extension I faced this error.
An error occurred while attempting to retrieve the list of local SharePoint sites configured with Reporting Services.
AX: Microsoft Dynamics AX 2012 R3 CU8
OS: Microsoft Windows Server 2012 R2
SQL: Microsoft SQL Server 2014
SP: Microsoft SharePoint Server 2013
Well, the first thing I checked was the event viewer, there was an access related issue with DB.
I opened the SSMS, Checked the service account, gave it sysadmin access and bingo! :)