cannot log to the system after modifing the connection string in the web config file.

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C#

ASP.NET

foreach (var cString in conectionstring)
{
   conectionString = cString;
   Configuration openWebConfiguration =WebConfigurationManager.OpenWebConfiguration("~");
   ConnectionStringsSection sections = openWebConfiguration.GetSection("connectionStrings") as ConnectionStringsSection;

   if (sections != null)
       {                              
       sections.ConnectionStrings["GihanBConnectionString"].ConnectionString = conectionString;
       ConfigurationManager.RefreshSection("connectionStrings");
       openWebConfiguration.Save();
       //Page.Response.Redirect(Page.Request.Url.ToString(), false); 
       //Response.Redirect(Request.Url.ToString()); 
       }
}

hi friends,
i have used this code to change my connection string at run time.its working.but the problem is,after modify, i cannot enter to the system.is it possible to do?

my purpose is to select database at run time for my asp.net web application.(multiple database for a web application).if some one can help me for this it will great for me.
thank you.