Q:

:observer.start throws an error

I'm trying to launch observer from iex, but I'm not sure why it isn't working. Some days ago, it worked without problems. I regularly update my Ubuntu with aptitude, so there could be the problem. Here is the error received from iex:
Erlang/OTP 20 [RELEASE CANDIDATE 2] [erts-9.0] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:10] [hipe] [kernel-poll:false]

Interactive Elixir (1.4.4) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> :observer.start

18:52:01.936 [error] WX Failed loading 'wxe_driver'@'/usr/lib/erlang/lib/wx-1.8.1/priv' 

{:error,
 {{:load_driver,
   'symbol _ZThn704_N17wxGenericListCtrl31GetSizeAvailableForScrollTargetERK6wxSize, version WXU_3.0 not defined in file libwx_gtk2u_core-3.0.so.0 with link time reference'},
  [{:wxe_server, :start, 1, [file: 'wxe_server.erl', line: 65]},
   {:wx, :new, 1, [file: 'wx.erl', line: 115]},
   {:observer_wx, :init, 1, [file: 'observer_wx.erl', line: 98]},
   {:wx_object, :init_it, 6, [file: 'wx_object.erl', line: 372]},
   {:proc_lib, :init_p_do_apply, 3, [file: 'proc_lib.erl', line: 247]}]}}

Any help?

Update:
There are weird things. I removed Elixir packages with aptitude. Then I have installed esl-erlang from erlang solutions repo (I think). The installed version is a RC version !!! Why? With that package some dependencies has been installed, like libwxbase-3.0. Afther that I have installed Elixir without dependencies. But observer is still not working. 
There is an erlang-observer package, but it cannot be installed with esl-erlang.
Thanks in advance

A:

Finally, I can find out a solution. I don't know why, but Erlang Solutions repo it's downloading 1.20-rc version of Erlang. I have downgraded to 1.6.3 (1.6.3.6 is not working either) and :observer is working again.

