Uninstall not complete

If BridgeDD has been deactivated, the only way that message could possibly occur is if you are using a PHP object cache (XCache, APC, APCu, memcached, etc) and/or a WordPress plugin that caches SQL queries (W3 Total Cache, WP Super Cache, etc).

Use of such programs in WordPress can have disastrous results because the admin panel is not updated correctly. You will need to disable the cache plugin and/or the PHP cache extension in order to deactivate BridgeDD (or I suspect, do much of anything in the admin panel).

If you are not using an object cache and/or a WordPress cache plugin, then the only other possible explanations are an obscure plugin conflict, an unsupported server setup, or file and/or database corruption. To proceed in this case, I would need to know the plugins you have installed and activated, as well as the hosting plan and version of WordPress you are using for your site.

EDIT: your name sounded familiar, so I looked at old support posts. As stated in a previous support message to you, BridgeDD requires WordPress 3.5 or greater, and I believe you were running an older version.

https://wordpress.org/support/topic/bridgedd-and-wpads

I checked again, and the last version of WordPress the WP-ADS plugin supported was 3.0. BridgeDD uses actions/filters that require WordPress 3.5. This is stated on the main plugin page as well as in the documentation.

Even if you have since updated WordPress, installing BridgeDD on an unsupported version might have caused the problem you are now having. I say might because I have not attempted to install BridgeDD on unsupported versions of WordPress, so I honestly do not know.

Does this only happen when you activate the security plugin, or does it happen when you activate any plugin? If only with the security plugin, I am curious whether it is detecting a database abnormality caused by the inappropriate installation of BridgeDD. If so, you should check whether the plugin can remove the abnormality it detected.

Sorry for taking a while to respond. I obtained a copy of WordPress 3.0 to see if I could duplicate your problem. And I was able to do so if BridgeDD was installed and activated in WordPress 3.0, then deleted without being deactivated. The problem persisted even after updating to WordPress 4.0, which mirrors your experience. (I will note that, as expected, BridgeDD did not work properly with WordPress 3.0 because some actions/filters required by BridgeDD did not yet exist.)

So we have two issues here. First, BridgeDD was installed on an unsupported version of WordPress. And second, BridgeDD was deleted without first being deactivated. I have no idea how to fix your problem. The one thing I do know is that it was not the fault of BridgeDD.

Perhaps someone familiar with older versions of WordPress will be able to assist you in removing whatever is in the database that is causing your problem.