Blogger Support has fixed the problem.
We've rolled back the change that caused issues you have observed, so you should be able to clear the cookies for www.blogger.com and fix the problem.
Now that the problem has been fixed, you'll probably get best results, if you're seeing these symptoms, by clearing cache, cookies, and sessions, then restarting the browser.
If you're able, you may possibly provide details that will help understand the reason for the problem.
- What specific number ("400", "403", "404") are you seeing?
- Where are you located (country, province / state, city)?
- What service provider do you use?
- What type of service is this? Cable ("television" network), Cellular Phone ("3g" / "4g" network), DSL ("voice" network), satellite, wi-max ("wireless to your home") will all contribute to this type of problem, in different ways.
- What operating system do you run (name, version), on your computer?
- What version of Blogger are you using? Draft (blue "B" logo) or Production (orange "B" logo)?
- What Blogger wizard are you using / trying to use?