Inserting a Column - Sometimes Works, Sometimes Not

I have had every part of this project working at some point, but for some reason Excel seems to decide every so often that it wants a different syntax for inserting a column. Initially, I used this:

targetCell.Select
MsgBox "Target Cell Selected", 0, "Got here"
Selection.EntireColumn.Insert
MsgBox "Column Inserted", 0, "Got here"

That worked great for a little while, then after working on some other parts of code, it changed its mind and for some reason decided not to like that syntax. It would select the correct cell, but wouldn't do the column insertion. In desperation, I tried a little re-ordering.

targetCell.EntireColumn.Select
MsgBox "Target Cell Selected", 0, "Got here"
Selection.Insert
MsgBox "Column Inserted", 0, "Got here"

This inexplicably worked, but I wasn't asking any questions. I kept working, and now it doesn't like either form, nor will it take

targetCell.EntireColumn.Insert

For context, let me explain the whole project. There's a sheet "instruments" that contains four columns: the vendor part number, the internal part number, the vendor name, and the row in the sheet "Sheet1" where the internal part number appears. There's a sheet "pivot" that comtains a column for each vendor and records the maximum number of vendor part numbers that correspond to one internal part number. Finally, there's a sheet "Sheet1" that has all the vendors as column headers and the internal part numbers in the leftmost column.

What I have to do is fill in Sheet1 - for every vendor-internal part number combination, put the vendor part number in the appropriate cell. In some cases there are duplicates, and in this case, we want to create an additional column for it. For instance,

----------- | VendorName
Internal P/N | ABC123, DEF456

Becomes

----------- | VendorName | VendorName2
Internal P/N | ABC123---- | DEF456

Here is all the code in its current form together:

Sub buildTable()
    Dim instrumentsSheet As Worksheet
    Dim sheet1Sheet As Worksheet
    Dim pivotSheet As Worksheet
    Dim targetCell As Range
    
    Application.ScreenUpdating = False
    Set instrumentsSheet = ThisWorkbook.Sheets("instruments")
    Set sheet1Sheet = ThisWorkbook.Sheets("Sheet1")
    Set pivotSheet = ThisWorkbook.Sheets("pivot")
    On Error GoTo what
    
    'Delete the existing data in all columns so that the macro can be run without
    '   creating extra columns accidentally
    sheet1Sheet.Range("B1:IV8155").Select
    Selection.Value = ""
    
    'Replace vendor headers
    Set targetCell = sheet1Sheet.Cells(1, 2)
    pivotSheet.Range("B1:CX1").Copy Destination:=targetCell
    
    'Go through and create all needed columns for every vendor (2 through 102)
    For i = 2 To 102
    
        'Parse through the maximum number of multiple entries for each vendor
        Vendor = pivotSheet.Cells(1, i).Value
        VendorMax = pivotSheet.Cells(2, i).Value
        
        'Create that number of columns for the vendor
        If (VendorMax > 1) Then
            For j = 1 To (VendorMax - 1)
        
                'Select the first row in that column
                VendorCol = Application.Match(Vendor, sheet1Sheet.Range("A1:IV1"))
                Set targetCell = sheet1Sheet.Cells(1, VendorCol + j)
            
                'Insert the column
                targetCell.EntireColumn.Insert
                MsgBox "Column selected", 0, "Got here"
                'Selection.Insert
                MsgBox "Column inserted", 0, "Got here"
                
                'Title the column
                Set targetCell = sheet1Sheet.Cells(1, VendorCol + j)
                targetCell.Value = Vendor & (j + 1)
            
            Next j
        End If
    Next i
    
    'Go through the vendor item numbers (2 to 38346)
    For i = 2 To 38346
    
        'Get the row that the internal part number is in
        PartRow = instrumentsSheet.Cells(i, 4).Value
        MsgBox PartRow, 0, "PartRow"
        
        'For each vendor item number, make sure that an internal part number exists
        If WorksheetFunction.IsNA(PartRow) = False Then
            
            'Set the target cell as the leftmost cell for the vendor in the internal part
            '   number row
            Vendor = instrumentsSheet.Cells(i, 3).Value
            'MsgBox Vendor, 0, "Vendor"
            VendorCol = Application.Match(Vendor, sheet1Sheet.Range("A1:IV1"))
            'MsgBox VendorCol, 0, "VendorCol"
            Set targetCell = sheet1Sheet.Cells(PartRow, VendorCol)
            
            'While the target cell has something in it, move the target cell one to the right
            Do While ((Len(targetCell.Value) = 0) = False)
                VendorCol = VendorCol + 1
                Set targetCell = sheet1Sheet.Cells(PartRow, VendorCol)
            Loop
            
            'Put the vendor part number in the target cell
            targetCell.Value = instrumentsSheet.Cells(i, 1).Value
            
        End If
        If i Mod 100 = 0 Then Debug.Print i

    Next i

    Application.ScreenUpdating = True
what:
    Debug.Print i
    
End Sub

I tried to comment it well enough that it would be obvious what each part is trying to do. If anyone has any ideas as to what the deuce is going on here, I would really appreciate some help. I just learned to program Excel macros yesterday, and this problem is really confusing the heck out of me.

Alright, apparently it's some odd formatting error that was caused by my clearing all of the cells in the first portion by setting their value to empty string. By using the Delete method instead, it works as desired.

Next you need to learn to debug. Did you know you can set breakpoints, monitor variables in the Watch window, single step through code, ...?

Much easier than all those MsgBox statements.