Created Unassigned: System.ArgumentOutOfRangeException: Specified argument was out of the range of valid values. [14999]

I am getting a weird issue: I am trying to copy a lot of formulas from another worksheet like the attachment.

1. When I debugging it, it seems that I can not get the formula. just like Cell[8,63].Formula is empty. But in fact I can see it in the cell.
2. After I clicked the cell and clicked Enter, I can get it.
3. If I do nothing, I will get the error like below:

Please help

System.ArgumentOutOfRangeException: Specified argument was out of the range of valid values.
Parameter name: Start cell Address must be less or equal to End cell address
at OfficeOpenXml.ExcelAddressBase.Validate()
at OfficeOpenXml.ExcelAddress.set_Address(String value)
at OfficeOpenXml.ExcelRange.get_Item(String Address)
at OfficeOpenXml.ExcelRangeBase.SplitFormula(Int32 ix)
at OfficeOpenXml.ExcelRangeBase.SplitFormulas()
at OfficeOpenXml.ExcelRangeBase.Set_Value(Object value, Int32 row, Int32 col)
at Com.Huawei.IT.iPlan.SP.Excel.RolloutPlanExcelHandler.ClearCell(ExcelRange cell)
at Com.Huawei.IT.iPlan.SP.Excel.RolloutPlanExcelHandler.<>c__DisplayClass22.<GetDataFromRolloutExcel>b__16(Int32 c)
at System.Collections.Generic.List`1.ForEach(Action`1 action)
at Com.Huawei.IT.iPlan.SP.Excel.RolloutPlanExcelHandler.GetDataFromRolloutExcel(List`1 dbColDefinitions, List`1 attributes, List`1 milestones, List`1 activePlans, Stream fileStream, PlanTypeEnum rolloutPlanTypeEnum, SaveResultModel& resultModel)
at Com.Huawei.IT.iPlan.SP.BLL.RolloutPlanBLL.ReadRolloutExcel(SPWeb spweb, Guid rolloutPlanId, SPFile file, List`1& attributes, List`1& milestones, List`1& activePlans, SaveResultModel& resultModel)
at iPlanTool.ProjectEvents.Events.RolloutPlanUpdatedEventReceiver.RolloutPlanUpdatedEventReceiver.ItemUpdated(SPItemEventProperties properties)