@Dollar Thanks for your reply! I had already looked at all these links.
The display name is "HL Apps" (no quotes), so it's not related to Kristin's post.
Starting RemoteApps from the web interface works by the way inside and outside the firewall. Existing Start Menus that had been populated prior to this problem also work. I can ping the single 2008 R2 sp1 server that's running everything, including RD Session Host, RD Licensing, RD Connection Broker, RD Gateway, and RD Web Access. The server is fully updated.
Everything seems to be working except for webfeed.aspx. I figured out what the mystery characters are: they are an exncrypted FormsAuthenticationTicket from WebFeedLogin.aspx. Specifically, this line...
Response.Write(FormsAuthentication.Encrypt(ticket));
Presumably, the FormsAuthenticationTicket should be processed by one of the pages, which would then result in XML. Thinking some application I installed screwed up an IIS configuration, I uninstalled and reinstalled RD Web Access. This appeared to have no affect. Short of any help, I'll do some more troubleshooting. It looks like the authentication configuration isn't quite right.
By the way, awesome first name, Dollar.