why ExcelWork.SaveCopyAs() function is used

sir,

        error is:->The remote procedure call failed. (Exception from HRESULT: 0x800706BE)

when running in visual studio gives correct result.. when run through IIS 8 gives error...

String FileName = "" + User.Identity.Name + ".xls";

ExcelWork.SaveCopyAs(strCurrentDir + FileName);
.....