Problem Creating Sql Express Database Programmatically

Hi all
this is my code and i find it in microsoft's site
if i run it with sql server connection it works but if i try to use it with sql express it give me this error:
CREATE FILE encountered operating system error 5(access denied) while attempting to open or create the physical file 'c://mydatabase.mdf'
it seems as a permission error but it isn't. I have to set something in sql express while in sql server it is already setted?


static void WriteDB()

{

String str;

//sql server connection

SqlConnection myConn = new SqlConnection("Server=localhost;Integrated security=SSPI;database=master");

//sql express connection
SqlConnection myConn = new SqlConnection("Server=localhost;Integrated security=SSPI;database=master");


str = "CREATE DATABASE MyDatabase ON PRIMARY " +

"(NAME = MyDatabase_Data, " +

"FILENAME = 'C:\MyDatabaseData.mdf', " +

"SIZE = 2MB, MAXSIZE = 10MB, FILEGROWTH = 10%) " +

"LOG ON (NAME = MyDatabase_Log, " +

"FILENAME = 'C:\MyDatabaseLog.ldf', " +

"SIZE = 1MB, " +

"MAXSIZE = 5MB, " +

"FILEGROWTH = 10%)";

SqlCommand myCommand = new SqlCommand(str, myConn);

try

{

myConn.Open();

myCommand.ExecuteNonQuery();

MessageBox.Show("DataBase is Created Successfully", "MyProgram", MessageBoxButtons.OK, MessageBoxIcon.Information);

}

catch (System.Exception ex)

{

MessageBox.Show(ex.ToString(), "MyProgram", MessageBoxButtons.OK, MessageBoxIcon.Information);

}

finally

{

if (myConn.State == ConnectionState.Open)

{

myConn.Close();

}

}

}


thanks
Marco