ref: http://devblog.rayonnant.net/2011/04/oracle-11g-r2-x64-client-with-odac.html?showComment=1322568025476#c9080251668350644709
when i run the command "OraProvCfg.exe /action:gac /providerpath:C:\Oracle\app\product\11.2.0\client_1\ODP.NET\bin\4\Oracle.DataAccess.dll"
the system says i need to install .net 4.0. when i had a quick look into the folder i found another one for 2.x so the logic is simple "4" is for .net framework 4 and "2.x" for earlier versions.
Hope this helps someone.