VBA Word - New text at start of document

You incorrectly set the value of oTable. I have highlighted the required changes in bold text.

Get into the habit of declaring variables. Check VBA > Tools > Options > Editor > Require Variable Declaration. This will add Option Explicit to the start of your new modules and this force you to declare the variables.

Option Explicit

Sub MyTest()

Const strTitle As String = "This is the title"
Const strInformation As String = "This is the info line"
Const strVersionDate As String = "Version Date"
Const strVersionNumber As String = "99"
Const strReviewer As String = "A N Other"
Const strApprover As String = "The Publication Editor"
Const strUnchanged As String = "Original text starts here ..."
Dim oDoc As Document
Dim oRange As Range
Dim oTable As Table
Dim oCell As Range
    ' -----------------------------------------------------------------------------
    ' Document title and information

    Set oDoc = ActiveDocument
    Set oRange = oDoc.Range
    oRange.Collapse wdCollapseStart
    oRange.InsertParagraphAfter

    With oRange
        .Text = strTitle & vbCr
        .Font.Size = 24
        .Font.name = "Arial"
        .Font.Bold = True
        .Font.Color = RGB(18, 75, 122)
        .Collapse wdCollapseEnd

        .Text = strInformation & vbCr
        .Font.Size = 10
        .Font.name = "Arial"
        .Font.Bold = True
        .Font.Color = RGB(0, 0, 0)
        .Collapse wdCollapseEnd
    End With

    ' -----------------------------------------------------------------------------
    ' Document table

    'GoTo SkipTable:
    Set oTable = ActiveDocument.Tables.Add(Range:=oRange, NumRows:=2, NumColumns:=2)

    With oTable.Range
        .Cells.Height = 20
        .Cells.VerticalAlignment = wdCellAlignVerticalCenter
        .Font.name = "Arial"
        .Font.Size = 10
    End With

    With oTable.Borders
        .InsideColor = wdColorAutomatic
        .InsideLineStyle = wdLineStyleSingle
        .OutsideColor = wdColorAutomatic
        .OutsideLineStyle = wdLineStyleSingle
    End With

    ActiveDocument.Variables("varName01").Value = strVersionDate
    ActiveDocument.Variables("varName02").Value = strVersionNumber
    ActiveDocument.Variables("varName03").Value = strReviewer
    ActiveDocument.Variables("varName04").Value = strApprover
    ActiveDocument.Fields.Update

    Set oCell = oTable.Cell(1, 1).Range
    oCell.End = oCell.End - 1
    oCell.Fields.Add oCell, Type:=wdFieldDocVariable, Text:="""varName01""", PreserveFormatting:=False

    Set oCell = oTable.Cell(1, 2).Range
    oCell.End = oCell.End - 1
    oCell.Fields.Add oCell, Type:=wdFieldDocVariable, Text:="""varName02""", PreserveFormatting:=False

    Set oCell = oTable.Cell(2, 1).Range
    oCell.End = oCell.End - 1
    oCell.Fields.Add oCell, Type:=wdFieldDocVariable, Text:="""varName03""", PreserveFormatting:=False

    Set oCell = oTable.Cell(2, 2).Range
    oCell.End = oCell.End - 1
    oCell.Fields.Add oCell, Type:=wdFieldDocVariable, Text:="""varName04""", PreserveFormatting:=False

    oRange.Start = oTable.Range.End
    oRange.Collapse wdCollapseEnd

SkipTable:
    ' -----------------------------------------------------------------------------
    ' Document original text

    oRange.Text = strUnchanged
    oRange.Font.Color = RGB(255, 0, 0)
    
    Set oRange = Nothing
    Set oCell = Nothing
    Set oTable = Nothing
    Set oDoc = Nothing
End Sub