to use emulator in in "code.appinventor.mit.edu" you need to install aistarter first.
after that you follow the instructions which contain the initializing update process.
for my lap that have 30 devices the initializing downloading process is stock
I have never encountered this error before. The aiStarter was built years ago, and it was used by many people. I trust it, but now I'm thinking if there are bugs in it.
I see the same version number (2.62) in ai2.appinventor.mit.edu and code.appinventor.mit.edu, so the Companion in ai2.appinventor.mit.edu should update for you, if there is a problem getting to the code server.