When SQL server enables the SA account, the Microsoft SQL Server Error Code 15535 is displayed. solution:

Use Microsoft SQL Server 2008 to connect to a server running Microsoft SQL Server 2005.

Open the Properties dialog box and enter the SQL server administrator account. Then, Run "sa" to log on to SQL Server Management studio. You have changed to "Sa logon attribute", and then click OK.

In this case, you will receive the following error message:

Title: Microsoft SQL Server Management Studio
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Failed to change logon 'sa. (Microsoft. sqlserver. SMO)
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Other information: exceptions that occur when a Transact-SQL statement or batch processing is executed. (Microsoft. sqlserver. connectioninfo)
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Creden cannot be set for the main SA. (Microsoft SQL Server, error: 15535)
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Cause

If the ing to certificate check box is not selected on the general logon properties-sa dialog box, this problem occurs. If selected, this check box does not indicate that SQL Server 2008 will try to delete any creden。 mapped to your login creden. Because your creden cannot be set to "sa" login, you will receive an exception message. When you click OK to close this dialog box

Solution
To solve this problem, make sure that the ing to creden check box on the General Tab Of the --- logon properties-sa dialog box is selected before changing the "sa" Logon attribute and clicking OK to close the dialog box.