SQL error i need HELP

04/28/2012 10:15 denis2112#1
TITLE: Microsoft SQL Server Management Studio Express
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Failed to retrieve data for this request. (Microsoft.SqlServer.Express.SmoEnum)

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ADDITIONAL INFORMATION:

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

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The server principal "Denis-PC\Denis" is not able to access the database "model" under the current security context. (Microsoft SQL Server, Error: 916)

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BUTTONS:

OK
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what do i do?