(See the best response by Lummox JR.)
AVG blocks BYOND from starting, gets stuck on ad screen. To fix it, disable AVG for the duration of your play. I normally completely close AVG, but that is just me. <3 You're welcome for the help.
If AVG is blocking BYOND, add it to the firewall exceptions and it wont do that anymore.
Best response
AVG is wet trash these days. I strongly recommend switching to anything else.
It's all a matter of opinion.
AVG has already said they sell information they collect to third-parties.
From article,
Here's the list of, what AVG calls, "non-personal data" the company claims to collect from its customers and sell to interested third-parties, specifically online advertisers:
  • Browsing History,
  • Search History,
  • Meta-data,
  • Advertising ID associated with your device,
  • Internet Service Provider (ISP) or Mobile Network you use to connect to AVG products,
  • Information regarding other apps you have on your device.

Previous policies allowed the firm to only collect:
  • Data on "the words you search",
  • Information about any malware on the users' machine.
If you're using avast! I can show you a walk through to how you can exclude all programs from both shields so that all components of BYOND run smoothly
Protip: AVG's software contains a keylogger and browser extension that spies on you which on some system configurations will interfere with BYOND's macros in games.

Not only that, but the portion of the program that does contain a keylogger does not uninstall itself when AVG is removed, and will attempt to reinstall itself over and over again after uninstallation.

Major components must be removed manually.

AVG is little better than a virus in 2016.
For the most part, microsoft security essentials in windows 7, or the built in windows defender in windows 8 and up cover anti-virus purposes just fine.

Also, something like 99% of viruses spread by attaching themselves to ads, getting adblock plus for your browser is practically enough for antivirus protection.