c# - Textfile data not importable to third party application -

i in process of developing windows application 3 textboxes, application reads instrument's serial number via serial port saves string , displays number on 1 of textboxes. user manually enters cpu number , mine number in other 2 textboxes , data saved in textfile importing third party app.if try import textfile doesn't work whereas if type in data manually textfile imports no problems if copy same manually typed text file , try import copy doesn't work also. furthermore observed if edit serial number textbox (the 1 form serial port) clearing , typing same serial number produced textfile imports correctly. sample output text file looks 71a04619010000c7,99080101,132 71a04615430000b9,99080101,132

is there difference between manually typing , using streamwriter?

private async void savebutton_click(object sender, eventargs e) {     string mydocpath = environment.getfolderpath(environment.specialfolder.mydocuments);     stringbuilder sb = new stringbuilder();      sb.append(serialnumbertextbox.text);     sb.append(",");     sb.append(cpunumbertextbox.text);     sb.append(",");     sb.appendline(minenumbertextbox.text);      using (streamwriter outfile = new streamwriter(mydocpath + @"\userinputfile.txt", true))     {         await outfile.writeasync(sb.tostring());     }  }