262144 (Win32 MB_TOPMOST) has no mapping in the .NET MessageBoxOptions enum, whose
only members are RightAlign/RtlReading/ServiceNotification etc., so PowerShell
rejected it: "cannot convert 262144 to MessageBoxOptions" (second failure of the
topmost attempt). Correct documented way is passing a TopMost invisible owner
form as the first argument of MessageBox.Show. Wrapped in try/catch that falls
back to a plain Show, so the dialog can no longer fail the node even if the
owner pattern misbehaves on some machine.