key dumplication when adding: httpmodules

Question

I am getting this error (it appears) when mod_mono auto restarts.Really need your help.

System.ArgumentException: Key duplication when adding: httpModules 
  at System.Collections.Hashtable.PutImpl (System.Object key, System.Object value, Boolean overwrite) [0x00000] in <filename unknown>:0 
  at System.Collections.Hashtable.Add (System.Object key, System.Object value) [0x00000] in <filename unknown>:0 
  at System.Collections.Specialized.NameObjectCollectionBase.BaseAdd (System.String name, System.Object value) [0x00000] in <filename unknown>:0 
  at System.Collections.Specialized.NameObjectCollectionBase.BaseSet (System.String name, System.Object value) [0x00000] in <filename unknown>:0 
  at System.Configuration.ConfigurationSectionCollection.get_Item (System.String name) [0x00000] in <filename unknown>:0 
  at System.Configuration.Configuration.GetSection (System.String path) [0x00000] in <filename unknown>:0 
  at System.Web.Configuration.WebConfigurationManager.GetSection (System.String sectionName, System.String path, System.Web.HttpContext context) [0x00000] in <filename unknown>:0 
  at System.Web.Configuration.WebConfigurationManager.GetSection (System.String sectionName, System.String path) [0x00000] in <filename unknown>:0 
  at System.Web.Configuration.WebConfigurationManager.GetWebApplicationSection (System.String sectionName) [0x00000] in <filename unknown>:0 
  at System.Web.HttpApplication.InitOnce (Boolean full_init) [0x00000] in <filename unknown>:0

I add as the first item below the entry in my web.config, and it's still happening. Please help me.