I am trying to enable Code First in my Visual Studio Web Express 2012. From what I have read so far I have to use the Package Manager Console and the command Enable-Migratio
This may be a late answer but this seems like it could be a permissions/access problem. Make sure that your project is not being opened from a mapped drive or similar.
If you are on a corporate network and logged into a domain, it is very likely that your user profile does not actually sit on your local computer but rather on the server. This will cause the same problem.
Try copy the project to your local c: and try again.