I have a database file .mdf from MS SQL EXPRESS in folder:
C:\\Program Files\\Microsoft SQL Server\\MSSQL10.SQLEXPRESS\\MSSQL\\DATA
I had this issue on Windows 2003 with SQL 2005. I had to take ownership of the files as my Windows user account and I got the database to attache that way.
You have to right click on the file, select Properties, click OK to get past the information screen, click the Advanced button, select your account from the listing of available accounts or groups, apply that change, and Click OK on the Properties screen. Once you have done all that you will be able to manage the file permissions.
I logged into SSMS with Windows Authentication and I was able to attach the database without error.
Cheers!