When you deploy your SSAS project in SQL 2012 then you might hit the error below.
Error 26 OLE DB error: OLE DB or ODBC error: Login failed for user ‘NT Service\MSSQLServerOLAPService’.; 28000
The issue is SQL 2012 (denali) installation configured MSSQLServerOLAPService to start the Analysis Service but somehow the user is not created in Windows.
I solved this problem by changing the Log on as to Local System account.