Carla plugin missing

Hello.

Thank you so much for making Qtractor!

I have used it to make some classical violin music, I couldn't have made it otherwise. However at some point Qtractor stopped working, specifically the sound was all wonky.. perhaps because of the new version update.. I'm bad with computers so please indulge me.. I waited for several months, doing other things, and perhaps that error has self-corrected, but now I can get no sound at all because, and this is the (hopefully only) problem I pose now:

When I go to the mixer, I see that none of my tracks have plugins. I used the plugin for Carla in the past, but it appears to be no longer available among the plugin selections, therefore evidently no sound is produced. I just need a plugin for an sfz soundfont file, then hopefully everything will work again.

https://drive.google.com/open?id=1yjrtflVRRtuar-Z2ZgwmqHyq34BSkr8l

As you can see I have only about twenty seconds of music, but it's quality stuff, and all made possible by you! :D Please if you have any suggestions I would be really grateful. I remember when I searched for an sfz-compatible plugin initially, I had great difficulty finding one that I could understand how to install and use on my Ubuntu system.

Thanks!