I just set it up. I brought up my extender and clicked Media Browser on the ribbon (or whatever it's called). I got this error: Access to the path C:/ProgramData/media browser/Styles_DoNotEdit.mcml is denied.
I figured the extender account probably need access to the directory. So on Windows 7 I right clicked Computer>Manage>Expanded Users and Groups, Clicked User, got the name of the extender account (the account with mcx in the name) and then went back to the C:/Programdata/media browser directory, right clicked, chose security, edit, clicked Add, and added the extender account. I gave it modify (I tried read and execute but that was not enough, it needs modify). If you add another extender to your Media Center, you need to repeat this process for the new MCX account on your Media Center.