Cannot attach the file *.mdf as database

Question

Basically I\'ve followed a tutorial and decided to delete the .mdf file afterwards.

Now whenever I try to run the application I get the following error

Answer 1

I didn't read all the responses, but if your .mdf file is NOT part of the SQL installation path, like C:\Temp, then the SQL Database Engine service account(s) will not have permission to create and write to the .ldf file or even read the .mdf file.

The solution is you have to give file system permissions to the SQL Server database engine service account that runs the SQL instance service. So for me, I gave permissions full control via Windows Explorer to my C:\Temp path that contained my .mdf file for the NT Service\MSSQL$SQLEXPRESS01 and NT Service\MSSQL$MSSQL2016 accounts.

Here is a Microsoft article that details this very issue.