It doesn't error here, but then I don't have all of your code and putting strAcronym in the find what field seems like nonsense to me.
Try:
Code:
Sub ScratchMacrop()
Dim oCol As New Collection
Dim lngIndex As Long
'A basic Word macro coded by Greg Maxey
Dim oRng As Word.Range
lngIndex = 0
Set oRng = ActiveDocument.Range
With oRng.Find
.Text = "<[A-Z]{3,4}>"
.MatchWildcards = True
While .Execute
On Error Resume Next
oCol.Add oRng.Text, oRng.Text
On Error GoTo 0
oRng.Collapse wdCollapseEnd
Wend
End With
For lngIndex = 1 To oCol.Count
MsgBox oCol(lngIndex)
Next lngIndex
End Sub