E.Yです。

別のパソコンで試みたところ、以下の文が出て、開発者に報告とでます。

System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index
   at System.ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument argument, ExceptionResource resource)
   at System.ThrowHelper.ThrowArgumentOutOfRangeException()
   at System.Collections.Generic.List`1.get_Item(Int32 index)
   at System.Collections.ObjectModel.Collection`1.get_Item(Int32 index)
   at RPPCAL.Models.Visitors.DBLoader.Visit(C調剤 調剤)
   at RPPCAL.Models.C調剤.Accept(ModelVisitor visitor)
   at RPPCAL.Models.Visitors.DBLoader.Visit(C処方せん 処方せん)
   at RPPCAL.Models.C処方せん.Accept(ModelVisitor visitor)
   at RPPCAL.Models.Visitors.DBLoader.Visit(C処方せん受付 受付)
   at RPPCAL.Models.C処方せん受付.Accept(ModelVisitor visitor)
   at RPPCAL.Models.Visitors.DBLoader.Visit(C患者 患者)
   at RPPCAL.Models.C患者.Accept(ModelVisitor visitor)
   at RPPCAL.Models.Visitors.DBLoader.Visit(C電子レセプト 電子レセプト)
   at RPPCAL.Models.C電子レセプト.Accept(ModelVisitor visitor)
   at RPPCAL.Views.MonthInputForm.LoadData(String month)
   at RPPCAL.Views.MonthInputForm.Do実行()
   at RPPCAL.Views.MonthInputForm.ProcessCmdKey(Message& msg, Keys keyData)
   at System.Windows.Forms.Control.ProcessCmdKey(Message& msg, Keys keyData)
   at System.Windows.Forms.Control.ProcessCmdKey(Message& msg, Keys keyData)
   at System.Windows.Forms.TextBoxBase.ProcessCmdKey(Message& msg, Keys keyData)
   at System.Windows.Forms.Control.PreProcessMessage(Message& msg)
   at System.Windows.Forms.Control.PreProcessControlMessageInternal(Control target, Message& msg)
   at System.Windows.Forms.Application.ThreadContext.PreTranslateMessage(MSG& msg)