How to pass error message in aspx page

   [WebMethod]
        public static string GetDEOIDCount(object qcAllocationDetails)
        {
            string resultMessage = string.Empty;
            Result result = null;
            IQCAllocation qcallocation = QBpoEntityCreator.GetQCAllocationEntity();
            try
            {
                qcallocation = qcAllocationDetails.ConvertToJsonString().JsonToObject(qcallocation.GetType()) as IQCAllocation;
                DisplayDEOIDCount = QbpController.GetDEOIDCount(qcallocation).Entity.ConvertToJsonString();

if (DisplayDEOIDCount == "" || DisplayDEOIDCount == null)
                {
                    ////DisplayDEOIDCount = show the message : Count is not present
                }
                if (result != null && result.Error.GetCount() > 0)
                {
                    resultMessage = result.Error.GetAll();
                }

            }
            catch (Exception exception)
            {
                resultMessage = string.Format("Technical error ocurred. {0}. Please contact to system administrator.", exception.Message);
            }

            return DisplayDEOIDCount;

        }