Runtime Error 5 при вызове BltFast (DirectDraw) - VB

ddsBack.BltFast CartToIsoX(dx, dy, W), CartToIsoY(dx, dy, H), Tiles(TileNo).Surface, Tiles(TileNo).TRect, DDBLTFAST_SRCCOLORKEY

Option Explicit
'размер карты в тайлах
Private mvarWidth As Integer, mvarHeight As Integer
'структура тайла. поверхность, ректангл
Private Type Tile
    Surface As DirectDrawSurface7
    TRect As RECT
End Type
'габариты тайла
Private mvarTileWidth As Integer, mvarTileHeight As Integer
'массив используемых на карте тайлов
Private Tiles() As Tile
'двухмерный массив карты тайлов
Private TileMap() As Integer
'количество используемых типов тайлов
Private mvarTilesQuantity As Integer
Public Property Let Height(ByVal vData As Integer)
    mvarHeight = vData
End Property
Public Property Get Height() As Integer
    Height = mvarHeight
End Property
Public Property Let Width(ByVal vData As Integer)
    mvarWidth = vData
End Property
Public Property Get Width() As Integer
    Width = mvarWidth
End Property
 
Private Sub LoadTiles(MapFile As String)
    SetConfigurationFile MapFile
    SetSection "Tiles"
    mvarTilesQuantity = Int(LoadValue("Quantity"))
    
    mvarTileWidth = Int(LoadValue("Width"))
    mvarTileHeight = Int(LoadValue("Heigh"))
    Dim i As Integer, j As Integer
    ReDim Tiles(mvarTilesQuantity)
    For i = 0 To mvarTilesQuantity - 1
        Set Tiles(i).Surface = CreateDDSFromFile(App.Path + LoadValue("Tile" + CStr(i + 1)))
        SetRect Tiles(i).TRect, 0, 0, mvarTileWidth, mvarTileHeight
    Next i
        
    ReDim TileMap(mvarWidth, mvarHeight)
    Dim S As String
    SetSection "TileMap"
    'i - y; j - x
    For i = 0 To mvarHeight - 1
        S = LoadValue("Y" + CStr(i + 1))
        For j = 0 To mvarWidth - 1
            TileMap(j, i) = Int(Left(S, 1))
            S = Right(S, mvarWidth - j - 1)
        Next j
    Next i
End Sub
 
Public Sub LoadMap(MapFile As String)
    SetConfigurationFile MapFile
    SetSection "Size"
    mvarWidth = Int(LoadValue("Width"))
    mvarHeight = Int(LoadValue("Height"))
 
    LoadTiles (MapFile)
End Sub
 
Public Sub DrawMap()
    DrawTiles
End Sub
 
Private Sub DrawTiles()
    Dim i As Integer, j As Integer
    For i = 0 To mvarWidth - 1
        For j = 0 To mvarWidth - 1
            'DrawTile i, j, Tiles(TileNo).Surface, Tiles(TileNo).TRect, mvarTileWidth, mvarTileHeight
            DrawTile i, j
        Next j
    Next i
End Sub
 
Private Sub DrawTile(X As Integer, Y As Integer)
    Dim TileNo As Integer
    TileNo = TileMap(X, Y)
    Dim dx As Long, dy As Long, W As Long, H As Long
    dx = CLng(X)
    dy = CLng(Y)
    W = CLng(mvarTileWidth)
    H = CLng(mvarTileHeight)
    ddsBack.BltFast CartToIsoX(dx, dy, W), CartToIsoY(dx, dy, H), Tiles(TileNo).Surface, Tiles(TileNo).TRect, DDBLTFAST_SRCCOLORKEY
End Sub