Cannot VBA write data to cells in Excel 2007/2010 within a function

From your comment above you wanted to try this approach

If you enter
=abb()
into any cell

Then cell A1 of that sheet wil be set to 12333

This is the line to update to pick the cell to update, and to place a value in it
Range("A1").Value = 122333

From I don't want my Excel Add-In to return an array (instead I need a UDF to change other cells)

I am reposting this piece of magic from Kevin Jones aka Zorvek as it sits behind the EE Paywall (link attached if anyone has access)

While Excel strictly forbids a UDF from changing any cell, worksheet, or workbook properties, there is a way to effect such changes when a UDF is called using a Windows timer and an Application.OnTime timer in sequence. The Windows timer has to be used within the UDF because Excel ignores any Application.OnTime calls inside a UDF. But, because the Windows timer has limitations (Excel will instantly quit if a Windows timer tries to run VBA code if a cell is being edited or a dialog is open), it is used only to schedule an Application.OnTime timer, a safe timer which Excel only allows to be fired if a cell is not being edited and no dialogs are open.

The example code below illustrates how to start a Windows timer from inside a UDF, how to use that timer routine to start an Application.OnTime timer, and how to pass information known only to the UDF to subsequent timer-executed routines. The code below must be placed in a regular module.

Declare Function SetTimer Lib "user32" ( _
      ByVal HWnd As Long, _
      ByVal nIDEvent As Long, _
      ByVal uElapse As Long, _
      ByVal lpTimerFunc As Long _
   ) As Long

Private Declare Function KillTimer Lib "user32" ( _
      ByVal HWnd As Long, _
      ByVal nIDEvent As Long _
   ) As Long

Private mCalculatedCells As Collection
Private mWindowsTimerID As Long
Private mApplicationTimerTime As Date

Public Function abb()

' This is a UDF that returns the sum of two numbers and starts a windows timer
' that starts a second Appliction.OnTime timer that performs activities not
' allowed in a UDF. Do not make this UDF volatile, pass any volatile functions
' to it, or pass any cells containing volatile formulas/functions or
' uncontrolled looping will start.

   abb = "Whatever you want"

   ' Cache the caller's reference so it can be dealt with in a non-UDF routine
   If mCalculatedCells Is Nothing Then Set mCalculatedCells = New Collection
   On Error Resume Next
   mCalculatedCells.Add Application.Caller, Application.Caller.Address
   On Error GoTo 0

   ' Setting/resetting the timer should be the last action taken in the UDF
   If mWindowsTimerID <> 0 Then KillTimer 0&, mWindowsTimerID
   mWindowsTimerID = SetTimer(0&, 0&, 1, AddressOf AfterUDFRoutine1)

End Function

Public Sub AfterUDFRoutine1()

' This is the first of two timer routines. This one is called by the Windows
' timer. Since a Windows timer cannot run code if a cell is being edited or a
' dialog is open this routine schedules a second safe timer using
' Application.OnTime which is ignored in a UDF.

   ' Stop the Windows timer
   On Error Resume Next
   KillTimer 0&, mWindowsTimerID
   On Error GoTo 0
   mWindowsTimerID = 0

   ' Cancel any previous OnTime timers
   If mApplicationTimerTime <> 0 Then
      On Error Resume Next
      Application.OnTime mApplicationTimerTime, "AfterUDFRoutine2", , False
      On Error GoTo 0
   End If

   ' Schedule timer
   mApplicationTimerTime = Now
   Application.OnTime mApplicationTimerTime, "AfterUDFRoutine2"

End Sub

Public Sub AfterUDFRoutine2()

' This is the second of two timer routines. Because this timer routine is
' triggered by Application.OnTime it is safe, i.e., Excel will not allow the
' timer to fire unless the environment is safe (no open model dialogs or cell
' being edited).

   Dim Cell As Range

   ' Do tasks not allowed in a UDF...
   Application.ScreenUpdating = False
   Application.Calculation = xlCalculationManual
   Do While mCalculatedCells.Count > 0
      Set Cell = mCalculatedCells(1)
      mCalculatedCells.Remove 1
      Range("A1").Value = 122333
   Loop
   Application.Calculation = xlCalculationAutomatic
   Application.ScreenUpdating = True
   End Sub

You cannot change cell A1 with a function in B2.

Visit: Description of limitations of custom functions in Excel . The text includes:

"A user-defined function called by a formula in a worksheet cell cannot change the environment of Microsoft Excel. This means that such a function cannot do any of the following:

• Insert, delete, or format cells on the spreadsheet.
• Change another cell's value. [My highlighting]
• Move, rename, delete, or add sheets to a workbook.
• Change any of the environment options, such as calculation mode or screen views.
• Add names to a workbook.
• Set properties or execute most methods."

Why do you want to change cell A1 in this way? Explain your objective and perhaps someone can help.

If you want to modify two cells with one formula, you may want to consider returning an array from your function. Here's an example:

Function abb()
    Dim arr As Variant
    ReDim arr(1 To 2)
    arr(1) = "aardvark"
    arr(2) = "bee"
    abb = arr
End Function

Select cells A2 to B2. Type =abb() and press ShiftCtrlEnter to specify that it is an array formula. This formula then modifies both cells (A2 and B2) at the same time.

Perhaps you can customise this to do what you want.