I recently ran into a problem trying to restore a SQL Server 2005 database to a Windows XP machine.  The database back up was created on a Windows Vista machine and I thought that the different OS versions was the culprit.  However, it turned out to be related to SQL server instances and folder paths.  Here is full error I received when I attempted to restore the database using SQL Server Management Studio:

Restore failed for Server 'localhost\sqlexpress'.  (Microsoft.SqlServer.Express.Smo)

Additional information:
System.Data.SqlClient.SqlError: The operating system returned the error '5(Access is denied.)' while attempting 'RestoreContainer::ValidateTargetForCreation' on 'c:\Program Files\Microsoft SQL Server\MSSQL.2\MSSQL\[my database name].mdf'. (Microsoft.SqlServer.Express.Smo)

I searched the Internet using the error message and found several posts stating that it was a problem with the privileges of the user account that my SQL Server Express service was running as. I hadn't changed the account it was running as and I had restored other databases in the past, but I checked the SQL Server Configuration Manager anyway.  As I suspected the service was still running as the default account (Network Service), so that wasn't it.   [more]

After I couldn't find a quick fix on the Internet I decided to look around the options in the Restore Database window.  It turns out the problem was with the paths under the restore options.  The backup was trying to restore the .mdf and .ldf files to the c:\Program Files\Microsoft SQL Server\MSSQL.2\MSSQL\ directory.  The instance of SQL Server I was working with was storing all it's data files in C:\Program Files\Microsoft SQL Server\MSSQL.1\MSSQL\Data\.  Once I changed the paths for the database file and log file to be the same as where my other database files were being stored the restore ran fine with no errors.  For additional reference, here is an article that explains the naming of folders for SQL Server 2005 instances: http://weblogs.sqlteam.com/tarad/archive/2006/06/07/10114.aspx