Here's some actual VB6 code. Can you spot the error that will cause the program to malfunction? 
The premise here: There are five locations, but the data is stored both in remote computers (locations 0-5) or on the local hard drive (6-11). Check_Stores contains the code to run on the data and is not part of the problem
Code:
Private Sub cmdStart_Click()
StatusBar1.Panels(1).Text = "Please wait....."
On Error GoTo ErrorHandler
StartNumber = 0 ' 1'st Number (0 or 6)
EndNumber = 5 ' 6th Item (Last Item 5 or 11)
LocationNumber = 0 ' Location Index (0-5)
optIndex = 0 ' Indicates location and whether remote (0-5) or local (6-11)
If chkAllStores.Value = Checked Then ' Do All Stores
If chkLocal.Value = Checked Then ' Use local files
StartNumber = StartNumber + 6
EndNumber = EndNumber + 6
End If
For optIndex = StartNumber To EndNumber
Option1(LocationNumber).Value = True
Call Check_Stores
LocationNumber = LocationNumber + 1
Next optIndex
Else 'Single Location
If chkLocal.Value = Checked Then optIndex = optIndex + 6 ' Use local files
Call Check_Stores
End If
ErrorHandler:
Select Case Err.Number
Case 0
' Do Nothing
Case 20
' Do Nothing
Case Else
MsgBox (Err.Number & " " & Err.Description)
Err.Clear
End Select
Resume Next
End Sub