The image is missing a frame. COMException (0x88982F62)

We have the following popup in a WPF application that should display two images returned from the internet, but throws the toys out with 'The image is missing a frame' when it hits EndInit()

Never come across this error before and can't find any explanation online that relates to this use - could it be an issue with the downloaded image, and if so how do I check it?

Thank you

Public Sub PopupModals_ChequeImages(ImageOne() As Byte, ImageTwo() As Byte)
    Try

        MainPopUp = New Window
        With MainPopUp
            .Width = 800
            .Height = 750
            .ResizeMode = ResizeMode.NoResize
            .Title = "Check Images"
            .Icon = BitmapFrame.Create(ReturnIconImage("GIF_ICO.ico"))
        End With
        MainPopUpGrid = New Grid
        NameScope.SetNameScope(MainPopUpGrid, New NameScope())

        Dim vGrid As New Grid
        For i As Integer = 0 To 2
            Dim vRow As New RowDefinition
            If i = 2 Then
                vRow.Height = New GridLength(35)
            Else
                vRow.Height = New GridLength(35, GridUnitType.Star)
            End If
            MainPopUpGrid.RowDefinitions.Add(vRow)
        Next

        Dim UpperSV As New ScrollViewer
        With UpperSV
            .VerticalScrollBarVisibility = ScrollBarVisibility.Auto
        End With
        Grid.SetRow(UpperSV, 0)
        MainPopUpGrid.Children.Add(UpperSV)


        Dim LowerSV As New ScrollViewer
        With LowerSV
            .VerticalScrollBarVisibility = ScrollBarVisibility.Auto
        End With
        Grid.SetRow(LowerSV, 1)
        MainPopUpGrid.Children.Add(LowerSV)

        'Convert the files and load into the scrollviewers'
        Dim vImage1 As New Image
        Dim vBitmap As New BitmapImage
        Using vStream As New IO.MemoryStream(ImageOne)
            With vBitmap
                .BeginInit()
                .CreateOptions = BitmapCreateOptions.PreservePixelFormat
                .CacheOption = BitmapCacheOption.OnLoad
                .StreamSource = vStream
                .EndInit()
                .Freeze()
            End With
            vImage1.Source = vBitmap
        End Using
        UpperSV.Content = vImage1

        Dim vImage2 As New Image
        vBitmap = New BitmapImage
        Using vStream As New IO.MemoryStream(ImageTwo)
            With vBitmap
                .BeginInit()
                .CreateOptions = BitmapCreateOptions.PreservePixelFormat
                .CacheOption = BitmapCacheOption.OnLoad
                .StreamSource = vStream
                .EndInit()
                .Freeze()
            End With
            vImage2.Source = vBitmap
        End Using
        LowerSV.Content = vImage2


        Dim DP As DockPanel = PopupStatusBar()
        Grid.SetRow(DP, 2)
        MainPopUpGrid.Children.Add(DP)
        StatusBarLoaded("Check images...")



        MainPopUp.Content = MainPopUpGrid
        MainPopUp.WindowStartupLocation = WindowStartupLocation.CenterOwner
        Dim CurApp As Application = Application.Current
        Dim vWindow As Window = CurApp.MainWindow
        MainPopUp.Owner = vWindow



        MainPopUp.ShowDialog()

    Catch ex As Exception
        EmailError(ex)
    End Try
End Sub

Full exception is

The image is missing a frame.
at System.Windows.Media.Imaging.BitmapDecoder.SetupDecoderFromUriOrStream(Uri uri, Stream stream, BitmapCacheOption cacheOption, Guid& clsId, Boolean& isOriginalWritable, Stream& uriStream, UnmanagedMemoryStream& unmanagedMemoryStream, SafeFileHandle& safeFilehandle)
at System.Windows.Media.Imaging.BitmapDecoder.CreateFromUriOrStream(Uri baseUri, Uri uri, Stream stream, BitmapCreateOptions createOptions, BitmapCacheOption cacheOption, RequestCachePolicy uriCachePolicy, Boolean insertInDecoderCache)
at System.Windows.Media.Imaging.BitmapImage.FinalizeCreation()
at System.Windows.Media.Imaging.BitmapImage.EndInit()
at HOAManagerClient051.PopupModals.PopupModals_ChequeImages(Byte[] ImageOne, Byte[] ImageTwo) in C:\Users\Dave\Documents\Visual Studio 2017\Projects\HOAManagerClient051\HOAManagerClient051\PopupModals.vb:line 3125
System.Runtime.InteropServices.COMException (0x88982F62): Exception from HRESULT: 0x88982F62

Images are returned like this

Await Task.Run(Sub()
    Using response As HttpWebResponse = DirectCast(request.GetResponse(), HttpWebResponse)
        Dim deserializer As New DataContractJsonSerializer(GetType(AllianceBank.CheckImageResponse))
        checkResponseObject = DirectCast(deserializer.ReadObject(response.GetResponseStream()), AllianceBank.CheckImageResponse)
    End Using
End Sub)

Dim frontImageRawGif As Byte() = Nothing
Dim backImageRawGif As Byte() = Nothing

Dim IsCheckImage As Boolean = True
Try
    frontImageRawGif = Convert.FromBase64String(checkResponseObject.FrontImage)
Catch ex As Exception
    IsCheckImage = False
End Try

Try
    backImageRawGif = Convert.FromBase64String(checkResponseObject.BackImage)
Catch ex As Exception
    IsCheckImage = False
End Try