método @GroupPrincipal FindByIdentity lança uma exceção estranha

Estou tentando obter todos os usuários pelo nome do grupo e exibi-lo no sharepart webpart. adGroupName algo como = "CompanyGroup".

GroupPrincipal grp = GroupPrincipal.FindByIdentity(ctx, IdentityType.Name, adGroupName);

Exceção

Para executar esta operação, uma ligação bem-sucedida deve ser concluída na conexão

Por que isso e o que estou fazendo de errado?

stack trace:

       at System.DirectoryServices.DirectoryEntry.Bind(Boolean throwIfFail)
   at System.DirectoryServices.DirectoryEntry.Bind()
   at System.DirectoryServices.DirectoryEntry.get_AdsObject()
   at System.DirectoryServices.PropertyValueCollection.PopulateList()
   at System.DirectoryServices.PropertyValueCollection..ctor(DirectoryEntry entry, String propertyName)
   at System.DirectoryServices.PropertyCollection.get_Item(String propertyName)
   at System.DirectoryServices.AccountManagement.PrincipalContext.DoLDAPDirectoryInitNoContainer()
   at System.DirectoryServices.AccountManagement.PrincipalContext.DoDomainInit()
   at System.DirectoryServices.AccountManagement.PrincipalContext.Initialize()
   at System.DirectoryServices.AccountManagement.PrincipalContext.get_QueryCtx()
   at System.DirectoryServices.AccountManagement.Principal.FindByIdentityWithTypeHelper(PrincipalContext context, Type principalType, Nullable`1 identityType, String identityValue, DateTime refDate)
   at System.DirectoryServices.AccountManagement.Principal.FindByIdentityWithType(PrincipalContext context, Type principalType, IdentityType identityType, String identityValue)
   at System.DirectoryServices.AccountManagement.GroupPrincipal.FindByIdentity(PrincipalContext context, IdentityType identityType, String identityValue)
   at NewCo.Intranet.Common.DataAccess.ADUserManager.GetUserForGroup(String adGroupName, Boolean recursive)
   at NewCo.Intranet.Common.DataAccess.ADUserManager.GetMemberForCurrentSite()
   at NewCo.Intranet.Components.WebParts.ADGroupMembers.ADGroupMembersUserControl.Page_Load(Object sender, EventArgs e)

DirectoryServicesCOMException {"Ocorreu um erro de operação. \ R \ n"}

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