Apologies for this issue. It is an unexpected consequence of the move from separate 32-bit/64-bit installers to a single unified installer in Opus 11.13.
I have updated the Silent Install guide with:
[ul][li]Details on how to do silent uninstalls. (Search for "/uninst" to find the new part.)
[/li]
[li]A note about the 11.12 -> 11.13 issue, to help others.[/li][/ul]