Make sure that you are running 32 bit (x86) version of Studio One. FerricTDS is a 32 bit plugin and will not load (like other plugins) in the x64 bit version of Studio One.
You can always remove the plugin, reset your Plugin Blacklist, then re-install the plugin.
Keep in mind, freeware Plugins often do not get updated over time, so there is always a chance that the plugin will stop loading. At which point you will have to contact the developer.