Why am I getting the error, "The function evaluated requires all thread to run"?

[tzz_12]

I am trying to rerun a script that I ran previously successfully, but now, I keep getting the error, "The function evaluated requires all thread to run" at the "management.AddIndex" method. There is probably a better way of writing the geoprocessing methods below, but I am relatively new at creating Add-In using the ArcGIS Pro SDK v2.8. Please see the script below: 

                var args2 = Geoprocessing.MakeValueArray(filePath, outGDB, fieldTable);
                GPRun("conversion.TableToTable", args2);

                //Create index to the field table - Error occurs here
                var ipara = Geoprocessing.MakeValueArray(fieldTable, "mukey", "tableIndex");
                GPRun("management.AddIndex", ipara);

         public async void GPRun(string GPTool, IReadOnlyList<string> parameters)
        {
            var gp_result = await Geoprocessing.ExecuteToolAsync(GPTool, parameters);
            if (gp_result.IsFailed)
            {
                if (gp_result.Messages.Count() != 0)
                {
                    Geoprocessing.ShowMessageBox(gp_result.Messages, "GP Messages", gp_result.IsFailed ? GPMessageBoxStyle.Error : GPMessageBoxStyle.Default);
                }
                else
                {
                    MessageBox.Show("Error in running the Geoprocessing Tool: " + GPTool + ", please check parameters.", "Geoprocessing Error");
                }
            }
        }

 Thanks for your help!