IIS Security Issue : Request for the permission of type 'System.Web.AspNetHostingPermission, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed.

hi I am Having 2 servers in load balancing. i have hosted my application in both the servers. When i browse it comes upto Login PAge and shows me the error 

Then  if Restart the IIS or REstart the App Pool it works fine for sometime and i receive the same later. 

Please Advice.