Baffling error in Background worker code

[Zomalaja]

Variables:
Source and Destination are both bitmaps that are the same size
hgt and wid are the height and width of the images minus 1

Here's the background worker Code:

Private Sub BGWProcess_DoWork(sender As Object, e As DoWorkEventArgs) Handles BGWProcess.DoWork`
  For Y = 0 To hgt
 For X = 0 To wid
If BGWProcess.CancellationPending Then Exit Sub
Destination.SetPixel(X, Y, Source.GetPixel(X, Y)) 'Here is where it fails
 Next
BGWProcess.ReportProgress(Y)
  Next
End Sub

Private Sub BGWProcess_ProgressChanged(sender As Object, e As ProgressChangedEventArgs) Handles BGWProcess.ProgressChanged
TxtProgress.Text = e.ProgressPercentage.ToString
PictureBox1.Image = Destination
End Sub

The exception is "System.InvalidOperationException: Object is currently in use elsewhere."
at the line "Destination.SetPixel(X, Y, Source.GetPixel(X, Y))
There is nothing else going on that might be accessing any of the bitmaps or the PictureBox. Any ideas would be greatly appreciated.