The .Net Framework has a feature called Shadow Copy.

Shadow copy is enabled on every appdomain created by ASP.NET by default. By default assemblies loaded will be copied to a shadow copy cache directory, and will be used from that location.

But this may create problem sometimes.

The following code snippet will help you to catch an error in the global.asax file,

Turn off the custom error mode in web.config file first,

<customErrors mode="Off">

And add this code in your global.asax file to catch the error,

void Application_Error(object sender, EventArgs e)
 {
 HttpContext context = ((HttpApplication)sender).Context;
 if (context.Error != null)
 {
 Exception ex = context.Error;
 string msg = string.Empty;

 while (ex != null)
 {
 if (!string.IsNullOrEmpty(ex.Message))
 msg += ex.ToString() + "<br /><br />";
 ex = ex.InnerException;
 }
 context.Response.Clear();
 context.Response.Write(msg);
 context.Response.End();
 }
 } 

Hope this helps