Listview Type mismatch

I have a form on which I have an array of 28 ListView boxes. These are used to display alphabetical lists controlled by a tab strip.

However when I run the code below which is used to read the data in from a datafile I am presented with the error: Runtime error'13': Type mismatch.

If any one has an idea what I am doing wrong it will be greatfully received.

VB Code:

Dim AtoZlstNum As ListItem
Dim AtoZlstLetter(27) As ListItem
 
For a = 1 To NumSongs
  Line Input #1, SongTitle(a)
  If InStr(1, SongTitle(a), ";", vbTextCompare) Then
    SplitText = Split(SongTitle(a), ";", 2, vbTextCompare)
    SongTitle(a) = SplitText(0)
    Set AtoZlstLetter(27) = lstAtoZ(27).ListItems.Add(, , Str(a))
    AtoZlstLetter(27).SubItems(1) = SplitText(1)
  End If
  b = Asc(Left(SongTitle(a), 1))
  If b > 46 And b < 58 Then
    Set AtoZlstNum = lstAtoZ(0).ListItems.Add(, , Str(a))
    AtoZlstNum.SubItems(1) = SongTitle(a)
  Else
    b = b - 64
    Set AtoZlstLetter(b) = lstAtoZ(b).ListItems.Add(, , Str(a))     <- Error occurs here
    AtoZlstLetter(b).SubItems(1) = SongTitle(a)
  End If
  ProgressBar1.Value = a
Next a

In advance Thank you

Type mismatch means you are passing a string value where numeric value is expected or vice versa...

I have checked that and does not matter if send number or text same error message produced at the same point.