So I'm the one who drove to Syphax. Just tried the website and was totally able to register. I also recently got this email:
UPDATE from Extended Day:
We greatly apologize for the inconvenience as the registration website is again experiencing issues. The developers are working to correct any issues and make the process faster.
Please send an email
extended.day@apsva.us with your student(s)'s name, school and requested sessions and we will process your registration. You will be contacted in the next few weeks with additional information.