C#_建立mdf失败_存取被拒

原本小弟我在WinCE上使用SqlCeEngine都挺好用的
奈何最近专案需要使用PC
於是我查了一下MSDN
以下是代码

String str;
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();
                    }
                }

但很不幸的出现
System.Data.SqlClient.SqlException(0x80131904): CREATE FILE於尝试开启或建立实体档案'C:\MyDatabaseData.mdf'时,发现作业系统错误 5(存取被拒。)。
CREATE DATABASE失败。某些列出的档案名称无法建立。请检查相关的错误。

我查过很多相关资料
但都无法得到正确解答
恳请各位大大指点迷津