Server 2008 r2 to server 2012 upgrade

hi experts,

I am trying to upgrade from server 2008 r2 sp1 evaluation to server 2012 but getting an error message
"Windows Server 2008 R2 Standard cannot be upgraded to Windows Server 2012 Standard Evaluation (Server with a GUI). You can choose to install a new copy of Windows Server 2012 Standard Evaluation (Server with a GUI) instead, but this is different from an upgrade, and does not keep your files, settings, and programs. You’ll need to reinstall any programs using the original installation discs or files. To save your files before installing Windows, back them up to an external location such as a CD, DVD, or external hard drive. To install a new copy of Windows Server 2012 Standard Evaluation (Server with a GUI), click the Back button in the upper left-hand corner, and select “Custom (advanced)”.

I ran /forestprep and /domainprep before installing it.

Any suggestions will be appreciated.