This is a common known problem caused by ModSecurity. ModSecurity is installed in your web host panel. What is being blocked by ModSecurity is the .htaccess filename literally: .htaccess. You can try contacting your web host and ask them to create a ModSecurity whitelist rule for this or use the steps below to delete the wp-admin .htaccess file in Quarantine.
1. Go the BPS Pro > Pro-Tools menu/page > DB Table Cleaner|Remover tool tab page.
2. Delete the quarantine database table by clicking the Drop Radio button for this database table: xx_bpspro_arq_quarantine
3. Click the Empty|Drop button to delete the BPS quarantine database table. A new empty BPS quarantine database table will be automatically created.
4. Use FTP or your web host control panel file manager and delete all folders under the BPS Quarantine folder located here: /wp-content/bps-backup/quarantine/