Snapshot technology error (0xE000037D): ON SQL

Hi

Ive gone into there and ive made sure the SA (system admin) account is there which is what i enetered in to BE12. ive added the required priviledges. now im getting an error from the amanagement studio when i select ok to apply the changes to the database

TITLE: Microsoft SQL Server Management Studio
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Add member failed for DatabaseRole 'db_datareader'.  (Microsoft.SqlServer.Smo)

For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&ProdVer=10.0.1600.22+((SQL_PreRelease).080709-1414+)&EvtSrc=Microsoft.SqlServer.Management.Smo.ExceptionTemplates.FailedOperationExceptionText&EvtID=Add+member+DatabaseRole&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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Lock request time out period exceeded.
Cannot use the special principal 'dbo'. (Microsoft SQL Server, Error: 1222)

For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&ProdVer=10.00.1600&EvtSrc=MSSQLServer&EvtID=1222&LinkId=20476

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BUTTONS:

OK
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Any further ideas?