Another weird thing: One of the servers which doesn't work (BLEEP) does work on the Public Server List by LabyMod...
Oops... But still doesn't work
Already did what Owendog77 said... I'm using 1.12.2 LabyMod, which worked fine a long time. My Username is Sn0wArmy_Crazy.
Hey there, when I tried to join to GTM today, it didn't work giving the error above. This applies only for 4 of the servers in my list, others work.