Why does SQL Server need permissions to access data and log files?
The SQL Server service account needs to have read/write access to the folders where the data and log files exist. Because it needs to read and write.

By default the service account has access only to SQL Server's own folder structure. This has nothing to do with what access you have.

Your options are:


Grant explicit read/write access to your desired folder/tree
Change the service account to be you
Put the database files in their proper location for that instance


I prefer the latter so that you don't have active database files scattered all over your machine.