Windows authentication denied asp.net -

i have tried search stack overflow time answer question without success.

i have asp.net mvc3 application windows authentication.

because of logging have know using application when access it, , therefore users being prompted typical login dialog when enter page can see using application.

when user enters his/her nt logging details system accept credentials , lets them use page. getting different information users active directory.

the page on intranet , being accessed computer logged on domain webpage denies, how prompting when user first enters page, , user enters his/her nt details mentioned earlier.

my problem system sometimes keeps denying users when try login computers.

i have checked of different things such anonymous identification , forth , shouldn't problems @ all.

i need place can see perhaps events or other log why being denied.

this how checking of roles has been made:

 public class financialreportcontroller : baseemployeecontroller { 

.

[authorizeallexceptshop] public class baseemployeecontroller : controller { } 

.

 public class authorizeallexceptshop : authorizeattribute {     protected override bool authorizecore(httpcontextbase httpcontext)     {         return !httpcontext.user.isinrole(constants.roles.shop);     } } 

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public static class constants {      public static class roles     {         public const string shop = @"internal\xp_shopusers_dk";     } 

my web config has line:

  <authentication mode="windows"></authentication> 

where login success audits. in domain can log success , failure audits. if maybe ad or local event logs login success attempts can log failure atempts.

never done web app not sure if help. shot in dark.

:}