It’s very possible that your school district has blocked access to Vimeo and Slideshare.  These are the sites where we host our videos and slide show presentations.  You will want to ask your district to please allow access to these sites and the following urls:

In addition, it's possible your school has web filters in place that restrict access on your computer or your students' computers.  Provide your school's technology department with the following urls and they can "whitelist" GrammarFlip and resolve the issue for you: