Red X shown in VB.NET chart - vb.net

Question

I have code that calculates stress at multiple points on a tank and then graphs these stresses on a Chart. I'll be viewing charts with no problem, and all of a sudden, the chart displays a red X and I need to close my program to view the stress results again.
I know there's no bug in my code. No exception is thrown. Any suggestions?
Public Sub Graph(Curves) 'Creates the Graphs
crtStressData.Series.Clear()
crtStressData.Legends.Clear()
'Dimension arrays for data points
FileClose()
Dim data As Double
Dim StressTitle As String
Dim k As Integer
Dim BorderSize As Integer = 4
'set up main graph
crtStressData.ChartAreas(0).CursorX.IsUserSelectionEnabled = True
crtStressData.ChartAreas(0).CursorY.IsUserSelectionEnabled = True
crtStressData.ChartAreas(0).AxisX.ScaleView.Zoomable = True
crtStressData.ChartAreas(0).AxisY.ScaleView.Zoomable = True
crtStressData.ChartAreas(0).AxisX.ScrollBar.IsPositionedInside = False
crtStressData.ChartAreas(0).AxisY.ScrollBar.IsPositionedInside = False
Dim LegendName As String = ""
StressTitle = TankName + " " + GraphType + " Stresses: " + strLoad + " Loading"
If GraphType = "Combined" Then
'Set component parameters
'Create Combined Graph
Call CreateDataPoints()
'Add title,
crtStressData.Titles(0).Text = StressTitle
For i = 0 To Curves - 1 'add legends
If i = 0 Then
LegendName = "Minimum Principal Stress"
ElseIf i = 1 Then
LegendName = "Minimum Principal Stress Location"
ElseIf i = 2 Then
LegendName = "Maximum Principal Stress"
ElseIf i = 3 Then
LegendName = "Maximum Principal Stress Location"
End If
crtStressData.Series.Add(LegendName)
''work on legend name
crtStressData.Series(i).ChartType = DataVisualization.Charting.SeriesChartType.Line 'sets as a line graph
crtStressData.Series(i).XAxisType = DataVisualization.Charting.AxisType.Primary
crtStressData.Series(i).YAxisType = DataVisualization.Charting.AxisType.Primary
crtStressData.Series(i).BorderWidth = BorderSize
For j = 0 To MaxDataPoints 'add points per legend type
'set up which data to add and define color
If i = 0 Then
' StressType(k) = "Minimum Principal Stress"
data = SMINMAXData(j)
color = Drawing.Color.Blue
ElseIf i = 1 Then
' StressType(k) = "Minimum Principal Stress Location"
data = SMINLOCData(j)
color = Drawing.Color.Green
ElseIf i = 2 Then
'StressType(k) = "Maximum Principal Stress"
data = SMAXMAXData(j)
color = Drawing.Color.DodgerBlue
ElseIf i = 3 Then
' StressType(k) = "Minimum Principal Stress Location"
data = SMAXLOCData(j)
color = Drawing.Color.Red
End If
'add data and color
crtStressData.Series(i).Points.AddXY(XPosData(j), data)
crtStressData.Series(i).Color = color
Next
k = k + 1
Next
Else ' GraphType = "Components"
crtStressData.Series.Clear()
'Set component parameters
'Create Component Graph
Call CreateDataPoints()
'Add title and axes labels
crtStressData.Titles(0).Text = StressTitle
For i = 0 To Curves - 1 'add legends
If i = 0 Then
LegendName = "Bending"
ElseIf i = 1 Then
LegendName = "Pressure (X)"
ElseIf i = 2 Then
LegendName = "Tension (X)"
ElseIf i = 3 Then
LegendName = "Total (X)"
ElseIf i = 4 Then
LegendName = "Pressure (Y)"
ElseIf i = 5 Then
LegendName = "Shear"
End If
crtStressData.Series.Add(LegendName) 'creates line
crtStressData.Series(i).ChartType = DataVisualization.Charting.SeriesChartType.Line 'sets as a line graph
crtStressData.Series(i).XAxisType = DataVisualization.Charting.AxisType.Primary
crtStressData.Series(i).YAxisType = DataVisualization.Charting.AxisType.Primary
crtStressData.Series(i).BorderWidth = BorderSize
For j = 0 To MaxDataPoints 'add points per legend
If i = 0 Then
'StressType(k) = "Bending"
data = SXBMAXData(j)
color = Drawing.Color.Blue
ElseIf i = 1 Then
' StressType(k) = "Pressure (X)"
data = SXPMAXData(j)
color = Drawing.Color.Green
ElseIf i = 2 Then
' StressType(k) = "Tension (X)"
data = SXTMAXData(j)
color = Drawing.Color.DodgerBlue
ElseIf i = 3 Then
'StressType(k) = "Total (X)"
data = SXMAXData(j)
color = Drawing.Color.Red
ElseIf i = 4 Then
' StressType(k) = "Pressure (Y)"
data = SYMAXData(j)
color = Drawing.Color.HotPink
ElseIf i = 5 Then
' StressType(k) = "Shear"
data = SSMAXData(j)
color = Drawing.Color.DarkOrange
End If
'add data and color
crtStressData.Series(i).Points.AddXY(XPosData(j), data)
crtStressData.Series(i).Color = color
Next
k = k + 1
Next
End If
'LEGEND
Dim StressLegend As Legend = New Legend()
StressLegend.IsDockedInsideChartArea = False
StressLegend.Docking = Docking.Bottom
StressLegend.Font = New Font("Gil Sans MT", 11)
StressLegend.TextWrapThreshold = 100
StressLegend.Alignment = StringAlignment.Center
crtStressData.Legends.Add(StressLegend)
crtStressData.Dock = DockStyle.None
crtStressData.Show()
End Sub