Stop Code Running If Fields Blank

Ok - really need some help here. I have searched and searched but i think my problem is slightly different to the ones i am finding.

Basically i have a form and i want to force users to fill in one out of 4 tick boxes. If none of them are ticked when they press the close button i want the form to stay open and a message box come up.

I can get the message box part to work but the form still closes down.

The reason for this is that when the form closes it goes to another form that is linked to it by a unique ID number. This works by the following code.

Private Sub BTN_INVIS_Click()

Dim stDocName As String
Dim stLinkCriteria As String

stDocName = "frm closure"

stLinkCriteria = "[issue ID]=" & Me![Issue ID]
DoCmd.OpenForm stDocName, , , stLinkCriteria

Exit_BTN_INVIS_Click:
Exit Sub

Err_BTN_INVIS_Click:
MsgBox Err.Description
Resume Exit_BTN_INVIS_Click

End Sub

What i have tried to do is insert a piece of code into the above to generate the message box so it now looks as follows:

Private Sub BTN_INVIS_Click()

If [Transport_Delivery_issue_] = False And [Process_issue_] = False And [Design_issue_] = False And [Supplier_issue_] = False Then

MsgBox "You must complete the liability box before you can close this issue"

Cancel = True

[Design_issue_].SetFocus

End If

Dim stDocName As String
Dim stLinkCriteria As String

stDocName = "frm closure"

stLinkCriteria = "[issue ID]=" & Me![Issue ID]
DoCmd.OpenForm stDocName, , , stLinkCriteria

Exit_BTN_INVIS_Click:
Exit Sub

Err_BTN_INVIS_Click:
MsgBox Err.Description
Resume Exit_BTN_INVIS_Click

End Sub

This code checks the boxes and generates the message box if none are ticked - that works great. However it doesnt stop the second part of the code (the move to the next form) from executing if the boxes arent ticked.

Would really appreciate it if someone could help me - i'm fairly new to coding so the whole database is a bit cobbled together (mostly with help from this forum!).