You might come across this error when trying to attach an existing MDF file.

TITLE: Microsoft SQL Server Management Studio
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Failed to retrieve data for this request. (Microsoft.SqlServer.Management.Sdk.Sfc)

For help, click: https://go.microsoft.com/fwlink?ProdName=Microsoft%20SQL%20Server&LinkId=20476

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ADDITIONAL INFORMATION:

An exception occurred while executing a Transact-SQL statement or batch. (Microsoft.SqlServer.ConnectionInfo)

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CREATE FILE encountered operating system error 5(Access is denied.) while attempting to open or create the physical file 'D:\Microsoft SQL Server\MSSQL\Data\AM8K.mdf'. (Microsoft SQL Server, Error: 5123)

For help, click: https://docs.microsoft.com/sql/relational-databases/errors-events/mssqlserver-5123-database-engine-error

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BUTTONS:

OK
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Please do the following:

Make sure currently logged in Windows/Domain user has access to the physical folder where the MDF file resides.

Start “Microsoft SQL Server Management Studio” as administrator.

Now, try to attach the MDF file, this should resolve the Access Denied error.