Implemented "The following multiparts are not installed....."

When I try joining the server I get "The following multiparts are not installed on this client: pr_100v, pr_f100v"


I was on the server sunday but now I can't seem to get on. I am using the FTB launcher because the MYM launcher didn't work for me. Also I tried deleting my horizions then re downloading it and that did not seem to fix the issue. I am sure the solution is simple but I am kind of a nooby when it comes to minecraft and modpacks. Ty for da halp

 

Still doesn't work now I just have a null when I try connecting.

 

try rename the horizons folder and re-download the mod pack

 

Redownloaded it and it didn't work, but after trying to connect to the server over and over again I somehow connected.....