Private Sub Command120_Click()
    DoCmd.OpenReport ReportName:="rpt_EODGraph", View:=acViewPreview, _
      OpenArgs:=Me!Text0.Value
End Sub

Private Sub Report_Open(Cancel As Integer)
    Dim ch As Chart
    Set ch = Me.Graph3.Object.Application.Chart 'This line generates the error
    ch.ChartTitle.text = OpenArgs
End Sub