I'll re-post here, just in case:
When I look in your repository it seems that the bot created the file for the next activity on the Cbeg-76-patch-1-2 branch. My suggestion is that you open a pull request from that branch to master, and see if once you correct that file, the course is back on track.
@Cbeg-76 the bot is specifically looking for the file to be in the `_posts` directory. It may be easier to unenroll from the course and start a fresh one. You can do so in the course page, near the top right.