why I can't remove guest in user database

Try to remove guest user and it prompt below error msgs, anyone know how do I remove this from user db ?

TITLE: Microsoft SQL Server Management Studio
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Drop failed for User 'guest'.  (Microsoft.SqlServer.Smo)

For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&ProdVer=9.00.3042.00&EvtSrc=Microsoft.SqlServer.Management.Smo.ExceptionTemplates.FailedOperationExceptionText&EvtID=Drop+User&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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User 'guest' cannot be dropped, it can only be disabled. The user is already disabled in the current database. (Microsoft SQL Server, Error: 15539)

For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&ProdVer=09.00.3073&EvtSrc=MSSQLServer&EvtID=15539&LinkId=20476

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BUTTONS:

OK
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