While Loop Object Error

I believe as a first step I was not correctly addressing the two named references, which I think I fixed. EndingMonth is an output cell of a formula and contains the number which I want to use as iterations of the macro, and FirstMonthHeading is the first cell I want a value in (A value of 1).

Sub Populate()
    Dim Counter As Integer
    Dim Ending As Integer
    Counter = 1
    Ending = Range("EndingMonth").Value
    Range("FirstMonthHeading").Select
    While Counter < Ending
        ActiveCell.FormulaR1C1 = Counter
        ActiveCell.Offset(0, 1).Range("FirstMonthHeading").Select
        Counter = Counter + 1
    Wend
    
    
End Sub

Your syntax for the offset is slightly wrong, and there's no need to use the FormulaR1C1 property or to select each cell in turn...

Sub Populate()
    Dim Counter As Integer
    Dim Ending As Integer
    Counter = 1
    Ending = Range("EndingMonth").Value
    While Counter < Ending
        Range("FirstMonthEnding").Offset(Counter-1,0).Value=Counter
        Counter = Counter + 1
    Wend
    
    
End Sub

That should work, provided both the named ranges exist.

I used the code, there was one slight issue as the named range was FirstMonthHeading instead of FirstMonthEnding, but it returned a 400 error as well. Even if I hardcode in a value instead of Ending, it won't run the macro.

I believe the error has something to do with the way Ending is defined, as when I comment that out and hardcode a value it runs fine.

I can confirm the only issue is that I can't suck the value of EndingMonth into Ending. I've refrenced it a bunch of different ways and can't get it to work.

Sub Populate()


    Dim Counter As Integer
    Dim Ending As Integer
    Counter = 1
    Ending = Int(EndingMonth)
    Range("FirstMonthHeading").Select
    While Counter < Ending + 1
        ActiveCell.FormulaR1C1 = Counter
        ActiveCell.Offset(0, 1).Select
        Counter = Counter + 1
    Wend
    
    
End Sub

If instead I say Ending = 12, it runs perfectly. What is the issue? The referenced cell is just a SUM function and displays a number.

No idea what the problem is - I've created a workbook with the exact code I posted in and it runs fine, even when I put a formula in the EndingMonth cell.

Try this, if your FirstMonthHeading cell is A1 and, say, your EndingMonth is in B2 use the code...

Sub Populate()
    Dim Counter As Integer
    Dim Ending As Integer
    Counter = 1
    Ending = Sheets(1).Range("B1").Value
    While Counter < Ending
        Sheets(1).Range("A1").Offset(Counter-1,0).Value=Counter
        Counter = Counter + 1
    Wend
    
    
End Sub

Change the ranges and the sheet numbers to match the format of your workbook and see if that works. If it does then there's something up with the way you've named the ranges.

That's it! Thank you so much, I just deleted the old name and made a new one, popped it in and it worked great.

Good stuff, just one of those things I guess. Glad you got it working.