Your code seems to select line 6 OK for me.
I followed the help at
https://msdn.microsoft.com/VBA/Word-...to-method-word
The problem seems to relate to the wdLine constant as
Code:
Set myRange = ActiveDocument.StoryRanges(wdMainTextStory).Characters(1)
myRange.MoveEnd unit:=wdWord
myRange.MoveEnd unit:=wdLine
selects the first word in the document but gives a bad parameter message when the unit is wdLine.