An exception occurred when trying to issue security token: The server was unable to process the request due to an internal error. For more information about the error, either turn on IncludeExceptionDetailInFaults (either from ServiceBehaviorAttribute or from the configuration behavior) on the server in order to send the exception information back to the client, or turn on tracing as per the Microsoft .NET Framework 3.0 SDK documentation and inspect the server trace logs..

check your web.config files

1) Central admin,

2) C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\WebServices\SecurityToken

3) Your web app

in my case some wiered content added to my config file. please see below which is highlated with yellow color.

Under RoleManager section

=========================================

<add name="c" type="Microsoft.SharePoint.Administration.Claims.SPClaimsAuthRoleProvider, &#xD;&#xA;Microsoft.SharePoint, Version=14.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />

Under Membership section

=========================================

<membership defaultProvider="i" userIsOnlineTimeWindow="15" hashAlgorithmType="">

      <providers>

        <clear />

        <add name="i" type="Microsoft.SharePoint.Administration.Claims.SPClaimsAuthMembershipProvider, &#xD;&#xA;Microsoft.SharePoint, Version=14.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />

      </providers>

    </membership>

remove unwanted data and iisreset.

it worked for me.