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Microsoft SQL Error 5171 occurs due to many reasons like MDF file corrupted, virus infection, power failure, etc.

Here, at Bobcares our Support Engineers take care of MS SQL errors frequently as a part of our Server Management Services.

In this article, we’re going to show you what causes “SQL server 5171 error”, and how we help to fix it.

Let’s get to work!

What causes Microsoft SQL Error 5171

This error usually appears when trying to login to SQL or while trying to restore the MS SQL database.

Microsoft SQL Error 5171

This happens due to different reasons and some of them are:

  • Virus infection
  • Power failure
  • Damaged drivers
  • MDF file corrupted or not recognized
  • Invalid registry entries

One of the main reasons for 5171 to occur is database corruption due to power failure, damage on drivers etc.

The 2 main scenarios where we can see MS SQL error 5171 is when there is….

  • Database corruption in mirrored database
  • Improper upgradation of database

Let’s see how we can hande different scenarios.


How to fix  Microsoft SQL Error 5171

MDF and NDF files are primary and secondary data files of an SQL database. The first page of the MDF file called header page sometimes become unrecognized by the SQL Server.

In such a case, the MDF file is not considered as a valid primary database file and leads to MS SQL error 5171.

Let’s see the different scenarios where this error appears.


Scenario1: Database corruption in mirrored database

This error occurs while we are using a mirrored database. We may encounter MS SQL error 5171 while we try to set the database online by excecting the command:


In this scenario, we follow the steps shown for fixing the error 5171.

  • Firstly, set the database principal.
  • After that, modify the file information using ‘ALTER DATABASE MODIFY FILE’ command.
  • Then stop the currently running instance of MS SQL Server.
  • Now, copy MDF and LDF database files to another directory. Right-click the database and select properties in SSMS in the files page for checking the path of the MDF and LDF files.
  • Finally, restart the SQL Server and attach the database files.

Note: We need to set the database mirroring again after this procedure as this process removes database mirorring.


Scenario 2: Improper upgradation of database

Another scenario in which SQL error 5171 appears is while performing a database upgrade. Error appears when trying to attach the databse again after upgrading the database by detaching the database.

Here we can fix the issue by attaching the database using sp_attach_db as shown:

sp_attach_db @dbname = N’mydb’,
@filename1 =
N’C:Program FilesMicrosoft SQL ServerMSSQL13.MSSQLSERVERMSSQLDatamydb_Data.mdf’,
@filename2 =
N’C:Program FilesMicrosoft SQL ServerMSSQL13.MSSQLSERVERMSSQLData mydb_log.ldf’;

This fixes the error.


[Need assistance in fixing Microsoft SQL errors? Click here to talk to our experts.]



In short, the major causes for Microsoft SQL Error 5171 are database corruption and improper upgradation of the database. Today, we discussed in detail the possible ways for fixing this error.

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