CREATE DATABASE permission denied in database 'master'

[C# Programming]

Hi,

I'm using Visual Studio 2008 and SQLExpress 2005.My OS system is win XP.I want to access my database from "C:\Program Files\Microsoft SQL Server\MSSQL.1\MSSQL\Data\Coupon Management.mdf".I am confused that it attacg database from App_data.When i run my program it show error
CREATE DATABASE permission denied in database 'master'.
Cannot attach the file 'C:\Inetpub\wwwroot\WebSite2\App_Data\Coupon Management.mdf' as database 'Coupon Management'.

here is my connection string
connectionString="Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\Coupon Management.mdf;Database=Coupon Management;Trusted_Connection=Yes;Persist Security Info=True;Integrated Security=False
Plz help.
thnx in advance