Hi, Alex.  I've experienced the same problem.  Sometimes even when I shutdown the IBM Lotus Notes client, reopen it, then try to launch Designer, it will still not open.  I've been able to get the Designer client to open by closing the IBM Lotus Notes client and then removing the workspace folder under the Notes data directory.  Now when you restart the Notes client, the workspace folder will get rebuilt and you should be able to start your Designer client.

Thanks Dave.  Haven't had to resort to deleting the Workspace yet.  Shutting down the Notes client and restarting it enables the Designer client to work again, although I think I'll remove the workspace anyway as a once-off and see if that fixes the problem longer term.

Alex