调试程序时总是提示如下错误?

Project bbgrt.exe raised exception class EoleException with message"发生未知错误"
,Precess stopped.Use step or run to continue.

      FieldByName('FBillno').asstring:=DataM.CreateBillNo;
      FieldByName('FDate').Value:=MainForm.CurrentDate;   *****光标停在这里
      FieldByName('FJhDate').Value:=MainForm.CurrentDate+8;
      FieldByName('Fuser').Value:=MainForm.UserId;