So no one else is getting this right now?
500 Internal Error Couldn't retrieve the HTML document because of server-configuration problems. Contact site administrator.
That is what 500 means. The server is broke and acknowledges your HTTP GET request, but is unable to reply to it.
This happens when work gets done on servers as they don't know where to find things until all the servers are back on and running.
For example the nameservers for WotC are currently on and taking requests, but the subdomain servers such as www, ww2, etc are being worked on offline so people aren't able to get to them and cause delays in the maintenance.
There are many other things that could cause a 500 error, but they are all problems with the servers and out of your control.
So you are not alone, and it just means that with the website down today for a scheduled upgrade, that they are actually performing the upgrade rather than stalling to do it later.
Maybe even they are adding the character builder to be ready for when there is a link to it as well as fixing cookie problems, PDF problems, etc.
But it is not your software doing it.
Now if Scott can get to the server, he might be coming from inside the network and that means only the outside world is cut off while it is being repaired.
So you are connecting correctly, but WotC computers don't currently know what you are trying to connect to for some reason.