In Inventor 2018 custom browser panes got their own dockable window so that they can be moved around by the user.
As a result your old code that was creating your new ActiveX based BrowserPane and was trying to activate it does not work anymore.
You need to find the DockableWindow that was created for your BrowserPane and make that visible - this action will also make it active:
Public Sub BrowserTest() Dim partDoc As PartDocument Set partDoc = ThisApplication.ActiveDocument Dim myBrowserPane As BrowserPane Set myBrowserPane = partDoc.BrowserPanes.Add("Test", "WMPlayer.OCX") ' First you have to make its container visible Dim uiMgr As UserInterfaceManager Set uiMgr = ThisApplication.UserInterfaceManager Dim dockWindow As DockableWindow Set dockWindow = uiMgr.DockableWindows(myBrowserPane.Name) ' This will also activate it dockWindow.Visible = True End Sub
This will achieve the same as clicking the + button in the UI and selecting your browser pane that way: