I just found this very useful feature for always running Construct 2 as administrator, enabling previewing on LAN. Here we go:
- Bring up the options menu (where you find "Run as administrator").
- Click on "Troubleshoot Compatability".
- Click on "Troubleshoot program".
- Check "This program requires additional permissions" and click "Next".
- Click on "Test the program" and click "Next".
- Finally, press "Yes, save these settings for this program" and click "Close". Ignore the error it gave you. It's not an issue.
I'm running Windows 8, so it might be different on your machine. Happy previewing!