Haydon Passive VGA Video Extenders HELP

Hi Everyone I have an issue after purchasing Haydon Passive VGA Video Extenders over Cat5e - the cat5e cable run is about 20 to 30 meters max, The screen flickers on and off - if I set the resolution low (1024x768) it works better but goes off after randomly from 10 seconds to 2 minutes for about 3 to 5 seconds (screen goes black). Any ideas? I have 3 cables running that way tested all 3 but it's still the same. tried it on a laptop too and the screen was a little better but still went off for about 5 seconds after a certain amount of time. Any ideas what it could be that's causing the issue as i need to do another run shortly but don't want the same issue to happen. Thanks for reading. Dave