GroupPrincipal method FindByIdentity arroja una extraña excepción

Estoy tratando de obtener todos los usuarios por nombre de grupo y mostrarlos en el elemento web sharepoint. adGroupName algo así como = "CompanyGroup".

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

Excepción

Para realizar esta operación, se debe completar un enlace exitoso en la conexión

¿Por qué es eso y qué estoy haciendo mal?

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 {"Se produjo un error de operaciones. \ R \ n"}