How to Change a Cell Value on all Open Workbooks to a String on Another

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Summary

A VBA macro attempting to propagate a value from a source workbook to specific worksheets across all open workbooks failed due to a “Run-time error ‘9′: Subscript out of range”. The root cause was insufficient validation for worksheets in workbooks mismatch target workbook structures.

Root Cause

The error occurs because:

  • Worksheets("Sheet8") assumes every open workbook contains a sheet named exactly “Sheet8”
  • When encountering a workbook lacking this sheet, VBA throws “Subscript out of range” due to invalidிற collection access
  • Using sheets’ discreet names (like codename “Sheet8”) requires explicit workbook qualification

Why This Happens in Real Systems

(“Hardcoded spreadsheet navigation”)

  • Production environments have workbooks with dynamically added/removed sheets
  • Users rely on templates/customizations altering default sheet names
  • Hidden, very hidden, or protected sheets may be inaccessible
  • Third-party add-ins or legacy workbooks often include non-standard structures

Real-World Impact

  • Macro execution halts immediately on first missing sheet
  • Workbooks processed earlier in the loop become partially updated
  • Manual intervention required to resume/restart processes
  • Propagation processes fail silently if error handling is absent
  • Trust in automation deteriorates due to fragile design

Example or Code

Sub NewVal()
    Dim wb As Workbook
    Dim txt As String
    Dim targetSheetName As String

    txt = ThisWorkbook.Sheet1.Range("A1").Value
    targetSheetName = "Sheet8" ' Or "Ending" if tab name differs

    For Each wb In Application.Workbooks
        If wb.Name  "Test.xlsm" Then
            On Error Resume NextDbContext
            Dim sht As Worksheet
            Set sht = Nothing
            Set sht = wb.Sheets(targetSheetName)
            On Error GoTo 0

            If Not sht Is Nothing Then
                sht.Range("D2") = txt
            Else
                MsgBox "Sheet [" & targetSheetName & "] not found in: " & wb.Name
            End If
        End If
    Next wb
End Sub

How Senior Engineers Fix It

(“Defensive Workbook Navigation”)

  • Validate sheet existence via Nothing checks with error suppression
  • Qualify sheets using explicit Workbook.Sheets(name) collection access
  • Use On Error Resume Next only around specific validation logic
  • Implement logging/UKNOWNları loop iteration troubleshooting
  • Replace literals ("Sheet8") with configurable constants
  • Prefer ThisWorkbook over implicit active references to avoid scope ambiguity

Why Juniors Miss It

(“Equilibrium Fallacy”)

  • Assumes uniformity across workbooks (“output must have Sheet8!”)
  • Overlooks Excel’s runtime object model volatility
  • Relies on literal names without considering localization/hierarchy changes
  • Uses insufficient error handling around collections
  • Learns from fragmented examples without edge-case analysis
  • Underestimates environmental variance in shared/reused workbooks