Are you starting your server with the jar file? Don't do that, start it with like Terminal or whatever it is on mac :/ (I'm not a mac user but i belieive this is how it should work.
Just to say: Everyone has like similar issues and most of the times it's just 2 files you need to download. It's scala-library.jar.stash and bcprov-jdk15on-148.jar.stash
I want to add the Waila Mod to my Big Dig but it seems like NEI has to be updated for that and because of that ChickenCore has to be updated and the EnderStorage and then my server needs updating as well. But when I'be done that I can't log in to it... What am I doing wrong?
Okay, this sounds like the issue with not starting the server with launch.bat Just double-click launch.bat to start the server instead of minecraft_server.jar or something else.
Well this is a very common problem, but there is an easy solution just add .stash in the URL and then when you have downloaded it you remove the .stash. Place the files in the lib folder if you didn't know that.