0.12.1を早速インストールしましたが、0.10.0からのniconicome.dbの上書きで
致命的なエラーが出るようです

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未処理例外 (UI スレッド)
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予期せぬエラーが発生しました。続けて発生する場合は開発者に報告してください。
プログラムの実行を継続しますか？
(An exception occurred while trying to create region objects.

- The most likely causing exception was: 'System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation.

---> Prism.Regions.Behaviors.RegionCreationException: An exception occurred while creating a region with name 'PlaylistTree'. The exception was: Prism.Ioc.ContainerResolutionException: An unexpected error occurred while resolving 'Niconicome.Views.Mainpage.Region.PlaylistTree.PlaylistTree'

---> Unity.ResolutionFailedException: Resolution failed with error: Exception has been thrown by the target of an invocation.

For more detailed information run Unity in debug mode: new UnityContainer().AddExtension(new Diagnostic())

---> System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation.

---> System.Windows.Markup.XamlParseException: プロパティ 'Prism.Mvvm.ViewModelLocator.AutoWireViewModel' の Set で例外がスローされました。

---> Prism.Ioc.ContainerResolutionException: An unexpected error occurred while resolving 'Niconicome.ViewModels.Mainpage.PlaylistTree.PlaylistTreeViewModel'

---> Unity.ResolutionFailedException: Resolution failed with error: Exception has been thrown by the target of an invocation.
（以下略）

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はい(Y) いいえ(N)
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データのインポートでもダメでした
従来（0.10.0）のバージョンとは別物と考えた方が良さそうですね