Object variable or With block variable not set (Arrays) - arrays

Question

For several projects now I've had this error flash up and completely ground my projects. In most cases, I've simply had to leave them and start a new, different one. Basically, I just want to be able to refer to every object on the form that matches certain criteria. In this case it's an arcade style game with four different game modes. There is a timer that creates the objects to be shot at and it works fine, either a PictureBox or a label depending on which mode. on creation it changes the tag of each object to "Obj" & whatever shape/maths number it is with a space in-between. But for some reason it won't create an array of sorts on a different timer tick event to move them.
I just need it to be able to constantly add and delete objects to shoot at, the adding and moving and deleting was working fine, but as in all my other cases with arrays this error just worms its way in and me and my seriously qualified IPT teacher can't figure it out. Why does it suddenly start doing it and how can I fix it? Attached is some of the code for the object move event.
Dim NumofObjsLeft As Integer = 0
For Each obj As Object In Me.Controls
If obj.Tag.Contains("Obj") Then
NumofObjsLeft += 1
If NumofObjsLeft <= 0 Then
Wav += 1
WaveStart = True
End If
Select Case GameMode
Case "Protector"
Select Case Curry
Case "Shapes"
If TypeOf obj Is PictureBox AndAlso obj.Tag.Contains("Obj") Then
obj.Left += 15
End If
Case "Maths"
If TypeOf obj Is Label AndAlso obj.tag.Contains("Obj") Then
obj.Left += 15
End If
End Select
EDIT: Just thought I'd add all the code for Shape Spawn and Move. I haven't finished the other half of the code for Shape Move cause I couldn't get the first part to work.
Private Sub tmrShapeSpawn_Tick(sender As System.Object, e As System.EventArgs) Handles tmrShapeSpawn.Tick
If WaveStart = True Then
Select Case Wav
Case 1
NumofObjs = Wave1
Case 2
NumofObjs = Wave2
Case 3
NumofObjs = Wave3
Case 4
NumofObjs = Wave4
Case 5
NumofObjs = Wave5
Case 6
NumofObjs = Wave6
End Select
If F < NumofObjs Then
Dim newPic As PictureBox = New PictureBox
Dim newLab As Label = New Label
Dim CorrectLabel As Label = New Label
Dim CorrectPictureBox As PictureBox = New PictureBox
CorrectPictureBox.Height = 75
CorrectPictureBox.Width = 100
CorrectLabel.AutoSize = True
CorrectLabel.BackColor = Color.Transparent
CorrectPictureBox.BackColor = Color.Transparent
CorrectPictureBox.SizeMode = PictureBoxSizeMode.Zoom
CorrectLabel.ForeColor = Color.Blue
CorrectLabel.Font = New Font("Goudy Stout", 60, FontStyle.Regular)
Select Case GameMode
Case "Protector"
Randomize()
If CorrectMade = False Then
CorrectLabel.Left = CorrectLabel.Width
CorrectPictureBox.Left = CorrectPictureBox.Width
CorrectLabel.Top = Int(Rnd() * (Me.Height - CorrectLabel.Height))
CorrectPictureBox.Top = Int(Rnd() * (Me.Height - CorrectPictureBox.Height))
End If
newLab.Left = newLab.Width
newPic.Left = newPic.Width
newLab.Top = Int(Rnd() * (Me.Height - newLab.Height))
newPic.Top = Int(Rnd() * (Me.Height - newPic.Height))
Case "Catcher"
Randomize()
If CorrectMade = False Then
CorrectLabel.Top = CorrectLabel.Height
CorrectPictureBox.Top = CorrectPictureBox.Height
CorrectLabel.Left = Int(Rnd() * (Me.Width - CorrectLabel.Width))
CorrectPictureBox.Left = Int(Rnd() * (Me.Width - CorrectPictureBox.Width))
End If
newLab.Top = newLab.Height
newPic.Top = newPic.Height
newLab.Left = Int(Rnd() * (Me.Width - newLab.Width))
newPic.Left = Int(Rnd() * (Me.Width - newPic.Width))
End Select
Select Case Curry
Case "Maths"
lblCriteria.Text = lstNum1.Items.Item(Wav - 1) & " " & lstOp.Items.Item(Wav - 1) & " " & lstNum2.Items.Item(Wav - 1) & " ="
If CorrectMade = False Then
CorrectLabel.Text = lstAns.Items.Item(Wav - 1)
CorrectLabel.Tag = "Obj " & lstAns.Items.Item(Wav - 1)
Me.Controls.Add(CorrectLabel)
CorrectLabel.BringToFront()
End If
Randomize()
newLab.Text = Int(Rnd() * 100)
newLab.Tag = "Obj " & newLab.Text
Me.Controls.Add(CorrectLabel)
CorrectLabel.BringToFront()
Case "Shapes"
Dim epahs As Integer
Dim sap As String
lblCriteria.Text = lstShape.Items.Item(Wav - 1)
If CorrectMade = False Then
CorrectPictureBox.ImageLocation = "Shapes\" & lstShape.Items.Item(Wav - 1) & ".png"
CorrectPictureBox.Tag = "Obj " & lstShape.Items.Item(Wav - 1)
Me.Controls.Add(CorrectPictureBox)
CorrectPictureBox.BringToFront()
End If
Randomize()
epahs = Int(Rnd() * 9)
Select Case epahs
Case 0
sap = "Square"
Case 1
sap = "Circle"
Case 2
sap = "Triangle"
Case 3
sap = "Rectangle"
Case 4
sap = "Oval"
Case 5
sap = "Hexagon"
Case 6
sap = "Star"
Case 7
sap = "Diamond"
Case 8
sap = "Trapezium"
Case 9
sap = "Rhombus"
End Select
newPic.ImageLocation = "Shapes\" & sap & ".png"
newPic.Tag = "Obj " & sap
newPic.SizeMode = PictureBoxSizeMode.Zoom
Me.Controls.Add(newPic)
newPic.BringToFront()
End Select
CorrectMade = True
F += 1
Else
WaveStart = False
End If
End If
End Sub
Private Sub tmrShapeMove_Tick(sender As System.Object, e As System.EventArgs) Handles tmrShapeMove.Tick
Dim CBA As Integer
Dim NumofObjsLeft As Integer = 0
For Each obj As Object In Me.Controls
If obj.Tag.Contains("Obj") Then
NumofObjsLeft += 1
If NumofObjsLeft <= 0 Then
Wav += 1
WaveStart = True
End If
Select Case GameMode
Case "Protector"
Select Case Curry
Case "Shapes"
If TypeOf obj Is PictureBox AndAlso obj.Tag.Contains("Obj") Then
obj.Left += 15
End If
Case "Maths"
If TypeOf obj Is Label AndAlso obj.tag.Contains("Obj") Then
obj.Left += 15
End If
End Select
For CBA = 0 To ABC Step 1
If Collision(obj, Missile(CBA)) Then
Missile(CBA).Visible = False
Missile(CBA).Enabled = False
If picExplosion1.Visible = True And picExplosion2.Visible = False And picExplosion3.Visible = False Then
picExplosion2.Visible = True
tmrExplosion2.Start()
CentreOn(obj, picExplosion2)
ElseIf picExplosion1.Visible = True And picExplosion2.Visible = True And picExplosion3.Visible = False Then
picExplosion3.Visible = True
tmrExplosion3.Start()
CentreOn(obj, picExplosion3)
ElseIf picExplosion1.Visible = False Then
picExplosion1.Visible = True
tmrExplosion1.Start()
CentreOn(obj, picExplosion1)
Else
End If
If obj.Tag.Contains(lblCriteria.Text) Then
lblScore.Text += 1
Else
lblLives.Text -= 1
End If
Me.Controls.Remove(obj)
End If
Next CBA
Case "Catcher"
Select Case Curry
Case "Shapes"
If TypeOf obj Is PictureBox AndAlso obj.Tag.Contains("Obj") Then
obj.Top += 15
End If
Case "Maths"
If TypeOf obj Is Label AndAlso obj.Tag.Contains("Obj") Then
obj.Top += 15
End If
End Select
If Collision(obj, picChar) Then
If obj.Tag.Contains(lblCriteria.Text) Then
Score += 1
Else
Lives -= 1
End If
Me.Controls.Remove(obj)
End If
End Select
End If
Next obj
End Sub

Answer 1

1) Use background worker instead of timer. Its built to interact correctly with the main form thread and handle control interactions a bit more cleanly. Timers are notoriously problematic for both main UI thread sync issues and exiting unexpectedly.
2) You have to handle the obj.Tag or obj being nothing. The easiest way is to add
If obj is Nothing OrElse String.IsNullOrWhitespace(obj.Tag) Then
Continue For
End If
...as the first statement after the For loop.

Answer 2

Righto, thanks to everyone who commented, replied. It seems to be working now with just that extra condition. Adding an if statement to check to see if the tag is empty before comparing the text.
Dim NumofObjsLeft As Integer = 0
For Each obj As Object In Me.Controls
If obj.Tag > "" Then
If obj.Tag.Contains("Obj") Then
NumofObjsLeft += 1
If NumofObjsLeft <= 0 Then
Wav += 1
WaveStart = True
End If
Select Case GameMode
Case "Protector"
Select Case Curry
ETC...................................................