The filenames of some of your mods suggests you are not getting them from official sources, please read my signature for more info on why this is a bad thing.
Endercrack's author has no idea about making their code sided.
Edit: Their item class's constructor has a DIRECT reference to a static method in their ClientProxy. ?♂️
That doesn't look like the whole log, do you have FTP access to your server? If so please provide your debug.log using one of the sites in my signature (I prefer Gist since their limit is HUGE, but they do require you to make a free account).