为什么我得到文件未找到异常？

Question

在form1中我正在做：

AnimatedGif.CreateAnimation();

AnimatedGif是一个新类：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using unfreez_wrapper;
using System.IO;

namespace ScreenVideoRecorder
{
    public static class AnimatedGif
    {
        private static UnFreezWrapper unfreez;
        private static FileInfo[] fi;
        private static DirectoryInfo di;

        public static void CreateAnimation()
        {
            unfreez = new UnFreezWrapper();
            List<string> files = new List<string>();
            di = new DirectoryInfo(@"D:\Testbmp");
            fi = di.GetFiles("*.jpg");
            for (int i = 0; i < fi.Length; i++)
            {
                files.Add(fi[i].Name);
            }
            unfreez.MakeGIF(files, @"D:\Testbmp\Animated.gif", 8, true);
        }

    }
}

在它甚至到达CreateAnimation方法中新类的第一行之前，它在form1中抛出异常就行了：

AnimatedGif.CreateAnimation();

Could not load file or assembly 'unfreez_wrapper.dll' or one of its dependencies. The specified module could not be found

System.IO.FileNotFoundException was unhandled
  HResult=-2147024770
  Message=Could not load file or assembly 'unfreez_wrapper.dll' or one of its dependencies. The specified module could not be found.
  Source=ScreenVideoRecorder
  FileName=unfreez_wrapper.dll
  FusionLog=""
  StackTrace:
       at ScreenVideoRecorder.AnimatedGif.CreateAnimation()
       at ScreenVideoRecorder.Form1.ExitApplication_Click(Object sender, EventArgs e) in d:\C-Sharp\ScreenVideoRecorder\ScreenVideoRecorderWorkingVersion\Form1.cs:line 200
       at System.Windows.Forms.ToolStripItem.RaiseEvent(Object key, EventArgs e)
       at System.Windows.Forms.ToolStripMenuItem.OnClick(EventArgs e)
       at System.Windows.Forms.ToolStripItem.HandleClick(EventArgs e)
       at System.Windows.Forms.ToolStripItem.HandleMouseUp(MouseEventArgs e)
       at System.Windows.Forms.ToolStripItem.FireEventInteractive(EventArgs e, ToolStripItemEventType met)
       at System.Windows.Forms.ToolStripItem.FireEvent(EventArgs e, ToolStripItemEventType met)
       at System.Windows.Forms.ToolStrip.OnMouseUp(MouseEventArgs mea)
       at System.Windows.Forms.ToolStripDropDown.OnMouseUp(MouseEventArgs mea)
       at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
       at System.Windows.Forms.ToolStrip.WndProc(Message& m)
       at System.Windows.Forms.ToolStripDropDown.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
       at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
       at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.Run(Form mainForm)
       at ScreenVideoRecorder.Program.Main() in d:\C-Sharp\ScreenVideoRecorder\ScreenVideoRecorderWorkingVersion\Program.cs:line 18
       at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
       at System.AppDomain.nExecuteAssembly(RuntimeAssembly assembly, String[] args)
       at System.Runtime.Hosting.ManifestRunner.Run(Boolean checkAptModel)
       at System.Runtime.Hosting.ManifestRunner.ExecuteAsAssembly()
       at System.Runtime.Hosting.ApplicationActivator.CreateInstance(ActivationContext activationContext, String[] activationCustomData)
       at System.Runtime.Hosting.ApplicationActivator.CreateInstance(ActivationContext activationContext)
       at System.Activator.CreateInstance(ActivationContext activationContext)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssemblyDebugInZone()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException: 

我看到我的项目中的dll文件引用了它，并且在调试和发布时也在我的硬盘上。