Error when moving directory on same server

You still have the redirect in place. Does that mean you moved everything back?

If so, follow this guide: https://codex.wordpress.org/Moving_WordPress#Moving_Directories_On_Your_Existing_Server

Ok, try the guide at https://codex.wordpress.org/Moving_WordPress#Moving_Directories_On_Your_Existing_Server one more time.

It’s likely a plugin or theme file is conflicting, so once the move is done, and if you still see the error of course, try manually resetting your plugins (no Dashboard access required). If that resolves the issue, reactivate each one individually until you find the cause.

If that does not resolve the issue, access your server via FTP or SFTP, navigate to /wp-content/themes/ and rename the directory of your currently active theme. This will force the default theme to activate and hopefully rule-out a theme-specific issue (theme functions can interfere like plugins).

You’re welcome!

Did you do steps 4, 5, and 6 first?

If so, try downloading WordPress again and delete then replace your copies of everything except the wp-config.php file and the /wp-content/ directory with fresh copies from the download. This will effectively replace all of your core files without damaging your content and settings. Some uploaders tend to be unreliable when overwriting files, so don’t forget to delete the original files before replacing them.