Error

{
  error_logger,
  {{2004,11,11},{19,28,4}},
  'Can\'t set long node name!\nPlease check your configuration\n',[]
}

{
  error_logger,
  {{2004,11,11},{19,28,4}},
  crash_report,
  [
    [
      {pid,<0.18.0>},
      {registered_name,net_kernel},
      {error_info,{error,badarg}},
      {
        initial_call,
        {gen,init_it,[gen_server,<0.15.0>,<0.15.0>,{local,net_kernel},net_kernel,{ejabber,longnames,15000},[]]}
      },
      {ancestors,[net_sup,kernel_sup,<0.8.0>]},
      {messages,[]},
      {links,[<0.15.0>]},
      {
        dictionary,
        [{longnames,true}]
      },
      {trap_exit,true},
      {status,running},
      {heap_size,610},
      {stack_size,21},
      {reductions,2761}
    ],
    []
  ]
}

Explanation

You are starting the Erlang node, and you specify a short node name with the option -name. This tries to set a long node name, but it do not work.

Solution

Try to specify the long node name:

erl -name ejabberd@server.net ...