我已找到问题和解决方案.在控制器中，一个识别图像尺寸的功能(对基于移动的应用程序应用了一些CSS规则)导致了问题.

I have found the issue and solution. In controller an function to identify the image dimension (to apply some css rule for mobile based app) was causing the issue.

System.Drawing.Image img = System.Drawing.Image.FromFile(Server.MapPath("~") + spe_Fil.ImagePath);

未放置img对象，因此应用了锁定.添加img.dispose()后，文件锁定问题得到解决.

the img object was not disposed and hence a lock was applied. After adding img.dispose(), file locking issue got resolved.