VBA - "End if without Block If Error"

Indentation is your friend.

Code:

Sub CheckWords()
Selection.HomeKey Unit:=wdStory
Dim FirstRound, InQuotes As Boolean
Dim WrongWordCount As Integer
Dim WordCount As Integer
Dim TestingWord As String
WrongWordCount = 0
UnusableWords = Array("i", "me", "you", "us", "we", "my", "mine", "our", "your", "can't", "won't", "should'nt", "you're")
FirstWord = True
InQuotes = False
Do Until Selection.Bookmarks.Exists("\EndOfDoc") = True
  If (FirstWord = False) Then Selection.MoveRight (2)
    Selection.MoveEndUntil Cset:=" ", Count:=10
    TestingWord = NoPunct(Selection)
    InQuotes = QuoteState(TestingWord, InQuotes)
    If InQuotes = False Then
      For WordCount = 0 To UBound(UnusableWords)
        If TestingWord = UnusableWords(WordCount) Then
          Selection.Range.HighlightColorIndex = wdYellow
          WrongWordCount = WrongWordCount + 1
        End If    
    End If    [i]This belongs to an If started before the For.  Bad nesting.[/i]
      Next WordCount
    FirstWord = False
Loop
MsgBox ("The Program has finished and found " & WrongWordCount & " unusable words.")

Specifically, your problem is that inside the loop between "For Wordcount" and "Next Wordcount" there is one If but two End If.