Hi David,
Sorry for the delay in getting back to you.
Please advise if you followed this procedure for adding a bypass rule for BulletProof Security here:
https://css-javascript-toolbox.com/support/topic/bulletproof-security-ajax-issue-and-resolution/
If you have not created the bypass rule for BPS and you no longer wish to use this, unfortunately deactivating the BPS plugin is not enough. You would need to reinstall the BPS plugin and use the plugin to recreate the default WordPress .htaccess files.
If you are having trouble with this, please email me temporary admin login details for your website here:
support@css-javascript-toolbox.com
Thanks,
Damian