If OMN macOS won't startup, the following should get you up and running again.
OMN keeps your data in ‘/Users/<Username>/Library/Application Support/Outdoor Map’Navigator’.
The ‘Library’ folder is usually a hidden folder. Here are the steps to open the folder.
1. Open Finder
2. Hold option key and click ‘Go’ menu. You should see a ‘Library’ menu item. If you don´t see it, use Go to Folder, and past in the following (without the quote marks): "~/Library/" and press Go.
3. You should now see the ‘Library’ folder contents.
4. Click into the ‘Application Support’ folder. You should now see ‘Outdoor Map Navigator’. Please open that folder.
5. You should find two files which we want to delete: settings.xml and omn.db - please delete them both.
6. Restart OMN, and it will now ask you to login and sync with Anquet Cloud