RTE 9: Subscript out of Range

[Ciao]

Public Sub CheckSprites()
Dim i As Long

i = 1

While FileExist(GFX_PATH & "sprites\" & i & GFX_EXT)
NumSprites = NumSprites + 1
i = i + 1
Wend

ReDim DDS_Sprite(1 To NumSprites)
ReDim DDSD_Sprite(1 To NumSprites)

ReDim SpriteTimer(1 To NumSprites)

End Sub

It highlights the part of the code thats red.

Any ideas on what to do to fix this error?