The EPiServer Mail installer fails with the following error on a CMS R2 SP1 site (Public templates). I have tried to copy the ui/util-folders from program files but it didn't help.
94297  ERROR EPiServer.Install.Wizard.Steps.CloserStep - Installation threw an exception.
System.ApplicationException: Install failed, can't determine EPiServer CMS UI path
at EPiServer.Install.EPiServerMail4300.Closer.ExecuteInstall(SqlTransaction transaction, IProgressForm progressForm)
at EPiServer.Install.EPiServerMail4300.Closer.Execute(SqlTransaction transaction, IProgressForm progressForm)
Try EPiServer Mail 4.4 instead.
Yes, I would also recommend you to use EPiServer Mail 4.4 instead. Should you for some reason not be able to upgrade you can check this blog and see if that helps.
The workaround described in the blog did the trick.
4.4 must have been released minutes after my download :)