I am no longer using bullet proof security
We are well aware of that. The problem is that BulletProof security actually adds files to your site, and those files remain even after you remove the plugin.
The files added by BPS are causing the problem, and you either need to remove them, or install the updated BPS so that it can modify them to not cause the problem anymore.
WordPress can only solve problems caused by WordPress itself. If some other code comes in and changes things and that causes problems, then WordPress isn't capable of detecting and working around that.
To solve the problem caused by BulletProof, you need to find and delete the .htaccess file in the /wp-admin folder. This will solve that specific issue.