private void RegisterError(AbstractCallback callback, CallbackEvent evt, AppInfo app, Exception e)
        {
            int       eSpaceId  = 0;
            int       tenantId  = 0;
            HeContext heContext = null;

            try {
                eSpaceId = (app != null? app.eSpaceId : 0);
                tenantId = (app != null && HttpContext.Current != null? app.Tenant.Id : 0);

                if (app != null)
                {
                    heContext = app.OsContext;
                }
            } catch {
            }

            int errors = 0;

            _errorsInCallbacks.TryGetValue(callback, out errors);
            _errorsInCallbacks[callback] = (errors + 1);

            ErrorLog.LogApplicationError(
                eSpaceId,
                tenantId,
                "Error invoking callback " + callback.GetType().FullName + " on event " + evt.ToString() + ": " + e.Message,
                e,
                heContext,
                "Callback");
        }