I have a vb.net 3.5 application using PrincipalPermission class to ensure a user is a member of a role. The code works for some groups in Active Directory domain but not others. 
At first I thought the space was an issue but I checked 'Domain Users' which worked. Running this code I am a member of App Group. 

```
Imports System.Security
Imports System.Security.Principal
Imports System.Security.Permissions

    Private Function DemandSecurity() As Boolean
        AppDomain.CurrentDomain.SetPrincipalPolicy(PrincipalPolicy.WindowsPrincipal)
        Dim principalGroup As New PrincipalPermission(Nothing, "App Group")
        Try
            principalGroup.Demand()
            Debug.Print("Demanding pricipal permissions for current user on 'App Group' role succeeded. ")
        Catch secEx As SecurityException
            Debug.Print("Security Exception - Demanding pricipal permissions for current user on 'App Group' role failed. ")

            Application.DoEvents()
            MessageBox.Show("Permission denied. Output: " & vbNewLine & secEx.ToString, "App - Security Exception", MessageBoxButtons.OK, MessageBoxIcon.Error, MessageBoxDefaultButton.Button1)

            Return False
            Exit Function
        End Try
        Return True
    End Function

```

The error output from secEx.ToString is 

> 
> "System.Security.SecurityException: Request for principal permission failed.
>  at System.Security.Permissions.PrincipalPermission.ThrowSecurityException()
>  at System.Security.Permissions.PrincipalPermission.Demand()
>  at App.My.MyApplication.DemandSecurity() in C:\Documents and Settings\me\My Documents\Visual Studio 2008\Projects\App\App\ApplicationEvents.vb:line 28
> 
> 
> The action that failed was:
>  Demand
>  The type of the first permission that failed was:
>  System.Security.Permissions.PrincipalPermission
> 
> 
> The first permission that failed was:
>  IPermission class="System.Security.Permissions.PrincipalPermission, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
>  version="1">
>  Identity Authenticated="true"
>  Role="App Group"/>
>  
> 
> 
> The demand was for:
>  IPermission class="System.Security.Permissions.PrincipalPermission, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
>  version="1">
>  Identity Authenticated="true"
>  Role="App Group"/>
>  
> 
> 
> The assembly or AppDomain that failed was:
>  mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
> 
> 
> 

Let me know if I need to include anything else.