Mod server or something is down ?

It’s possible the server itself hasn’t synchronized with LFS master server

same problem with all the servers

which mod?
just one or all.

Happens when you update your mod and trying to join the track right after that. Just wait a bit (1 minute usually) and it will work

Quote from iiiiil :

Happens when you update your mod and trying to join the track right after that. Just wait a bit (1 minute usually) and it will work

Yup, or sometimes you can fix it by pitting out with another mod and trying again with the one that the host didn't know.

Edit: My guess is that it takes some time to transfer the new mod update from LFS.net to LFS server data.