A lot of people are reporting in official Blogger forums about this problem. Most of them, when try to create a new post, receive notorious bx errors (bX-xovb7t). Thanks to the rapid feedback, a Blogger employee Gatsby has finally given the solution in the forums but you can see it here.
=> Official fix from Blogger
1- Go to Settings | Formatting. troubleshoting
2- Scroll down and see the last option Post Template, it has a small box in front of it, remove any code in that box.
3- Click SAVE SETTINGS button.
4- That's it.
Note: If you've installed a classic Read More hack, then you might have some code in Post Template box. If you don't want to remove that code then you need to properly close all the tags in it. If you're not comfortable with that, leave me a comment, I'll be happy to help you.