Propagation: Mold or Fungus grew and DESTROYED my Jiffy Greenhouse - HELP, 1 by SabrinaW

SabrinaW wrote:
This is my very first time attempting to garden and I now have the feeling I'm not going to do well. I'm going to give it one more try though and if anyone can offer any advise to me I would be so happy.
I started with a Jiffy Professional Greenhouse and followed the instructions to the "T" with beautiful resulst in just a few days. But then after about 2 weeks I started to see small white fuzzy weblike groths. I removed the lid because the seedlings were starting to push it up and with in a week everything was DEAD (see picutre).
If there is anyone who can help me understand what I did wrong and what I can do to avoide this happening again that would be great. I'm going to restart a new tray today so, please, bring on the suggestions!