When developing applications, quite often you end up experimenting with different toolbar icons to test how well they serve their purpose. If you change an icon in an ImageList, you have to de-assign this ImageList from your toolbar and you lose all your image assignments. Instead of doing this repeatedly, use the same key values in your buttons and images.
Use this code to assign images to your buttons. For me it has been a time-saver:
Dim myButton As ButtonOn Error Resume NextWith Toolbar1 .ImageList = ImageList1 For Each myButton In .Buttons myButton.Image = myButton.Key NextEnd With