drawing PNG images with GDI+ causes out of memory exception

I'm trying to draw PNG images in the OnPaint event of a usercontrol I created.
The files are loaded from disk into an ArrayList using Image.FromFile.
I get very unexpected results, sometimes loading the ArrayList produces an error, other times the application crashes in the OnPaint event. The files are quite small: 5MB at the most, in total no more than 50MB is loaded. The error is always OutOfMemoryException.

When I convert the PNG's beforehand to Bitmaps, the size of course increases dramatically, to several hundred MB. This however works brilliantly, no errors and even acceptable performance. But I can't the bitmaps because I need the transparency of the PNG format. And for other reasons too I have to use the PNG's.

What's wrong with PNG and GDI+?
Any pointers appreciated.

VB.NET, Visual Studio 2005, .NET 2.0

Protected Overrides Sub OnPaint(ByVal e As PaintEventArgs)
        Try
            If Not mImageList Is Nothing Then
                e.Graphics.TranslateTransform(AutoScrollPosition.X, AutoScrollPosition.Y)
                e.Graphics.MultiplyTransform(Transform)
                For i As Integer = 0 To mImageList.Count - 1
                    e.Graphics.DrawImage(CType(mImageList.Item(i), Image), 0, 0)
                Next
            End If
        Catch ex As Exception
            Windows.Forms.MessageBox.Show(ex.ToString)
        End Try
    End Sub

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