用C#连接数据库时出现的问题

未处理 System.Security.SecurityException
  Message="请求“System.Data.SqlClient.SqlClientPermission, System.Data, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089”类型的权限已失败。"
  Source="mscorlib"
  StackTrace:
       在 System.Security.CodeAccessSecurityEngine.Check(Object demand, StackCrawlMark& stackMark, Boolean isPermSet)
       在 System.Security.PermissionSet.Demand()
       在 System.Data.Common.DbConnectionOptions.DemandPermission()
       在 System.Data.SqlClient.SqlConnection.PermissionDemand()
       在 System.Data.SqlClient.SqlConnectionFactory.PermissionDemand(DbConnection outerConnection)
       在 System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory)
       在 System.Data.SqlClient.SqlConnection.Open()
       在 王鹏翀.Form3.queding_Click(Object sender, EventArgs e)
       在 System.Windows.Forms.Control.OnClick(EventArgs e)
       在 System.Windows.Forms.Button.OnClick(EventArgs e)
       在 System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
       在 System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
       在 System.Windows.Forms.Control.WndProc(Message& m)
       在 System.Windows.Forms.ButtonBase.WndProc(Message& m)
       在 System.Windows.Forms.Button.WndProc(Message& m)
       在 System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       在 System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       在 System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
       在 System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
       在 System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(Int32 dwComponentID, Int32 reason, Int32 pvLoopData)
       在 System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
       在 System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
       在 System.Windows.Forms.Application.Run(Form mainForm)
       在 王鹏翀.Program.Main()
       在 System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args)
       在 System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       在 Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       在 System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       在 System.Threading.ExecutionContext.runTryCode(Object userData)
       在 System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)
       在 System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
       在 System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       在 System.Threading.ThreadHelper.ThreadStart()
  InnerException: 
挺悲剧的  搞来搞去都是这些问题 连接数据库  自己也不会排查问题