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Make sure you have the same mod versions and the same forge version. If you do not have the same exact mod and versions same goes for forge it will not work. It happened with me and friend so I checked her mods and my mods and we had different versions so I made sure we had the same mod versions as aternos provides and it worked.
thank you so much!!! it worked 
now it wont connect at all.. it shows that its online but it just wont let me join the server, all of my friends can
Just do what the error message tells you to do...
what do you mean? read aternos.org/connect ?
in other cases this pops up
could this be a problem too?
Can't keep up! Did the system time change, or is the server overloaded? Running 3541ms behind, skipping 70 tick(s)
here's my log https://mclo.gs/7Mhm4Mu
anyone care to help?
so i started an 1.12.2 forge server which has couple of mods on it and im playing with my friend and my sister who lives in the same house with me. so i joined the server and everything was fine except my sister couldnt get on it. it said io.netty.channel.AbstractChannel$AnnotatedConnectException: Connection timed out: no further information. so i tried to restart the server a couple of times, even flushed dns cache on her pc and nothing couldnt work. so i got out the server and went to the bathroom and she decided to try to get on the server again and it worked. i came back and tried to join again but i got the same message.. what could this mean? i've been playing vanilla with her and everything seemed to be working just fine
