Some schools require that you be on the school's network in order to submit electronically. You may need to be at school for Exam4's network connection to work. It is also possible your security software (such as Norton Internet Security) is blocking the transmission. Try disabling this for a brief time and attempt to submit the exam while it is turned off.
In some rare cases with macOS this can be caused by Safari's Caching mechanism. If you are on a mac try to Clear the History of Safari and see if that makes a difference.
- Launch Safari
- From the Safari Menu choose Clear History...
- Select all history from the Clear drop down then click Clear History