Value does not fall within the expected range. Microsoft.Office.Interop.Word

Hi, I have already asked this question on MSDN here, but didn't find any solution! 

starting new thread! 

I am having following exception in my project having Microsoft Interops, Com Ad in for Office, When assigning

fldTemp.Result.Font = currRange.Font;
//where currRange is instance of Word.Range 
//and   fldTemp is instance of Word.Field ;

System.ArgumentException: Value does not fall within the expected range.

   at Microsoft.Office.Interop.Word.Range.set_Font(Font prop)
   at xxx.yyy.ThisIsMyFun(args)

same piece of code running on some machines!

what's wrong? 

Kind regards