Error Caught in Page_Error event (BasePage.cs)

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Error in: https://www.bowling-stats.com/Page/Manage/AllUsr/ManLeagueStandingsDownload.aspx?IdLeague=10817
Error Message: ExcelTpl.GenerateStatsOnAllStandings() --> ExcelStanding.WriteStatsDataTable() --> Specified cast is not valid.
Stack Trace:
at Page_Manage_ManLeagueStandingsDownload.Page_Load(Object sender, EventArgs e) at System.Web.UI.Control.OnLoad(EventArgs e) at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)