Getting Error while Attaching the Database in SQL Server

You need to provide the modify privilege to the SQL Service accounts to the folder C:\ArrowSQL\Arr@Data and then attach the db, it will attach without privilege error!!
Now, if you are using windows 7. Open the SSMS like this – Right click -> Run as Administrator and then login in windows mode and try to attach the database files.

Please make sure that .mdf file and .ldf file on the same drive

What may the possible reasons for this error?

The problem of operating system error 5(access is denied.) is due to lack of permissions for SQL Server to access the Primary (.mdf) & Log (.ldf) files.

And to fix this error
Change the MSSQLSERVER service startup user account, with the user account who have better privileges on the files and then try to attach the database.
Or
Startup with windows administrator account, and open SQL Server with run as administrator option and try to login with windows authentication and now try to attach the database.