I keep getting this kind of error, in several modules.

It looks related with translations and unicode.

I have updated the server with --update=all, no effect. 

Any idea how to solve it?

2015-03-18 00:33:33,232 20597 ERROR mydatabase openerp.http: Exception during JSON request handling.
Traceback (most recent call last):
File "/opt/odoo/odoo_8_ocb/src/OCA/OCB/openerp/http.py", line 530, in _handle_exception
return super(JsonRequest, self)._handle_exception(exception)
File "/opt/odoo/odoo_8_ocb/src/OCA/OCB/openerp/http.py", line 567, in dispatch
result = self._call_function(**self.params)
File "/opt/odoo/odoo_8_ocb/src/OCA/OCB/openerp/http.py", line 303, in _call_function
return checked_call(self.db, *args, **kwargs)
File "/opt/odoo/odoo_8_ocb/src/OCA/OCB/openerp/service/model.py", line 113, in wrapper
return f(dbname, *args, **kwargs)
File "/opt/odoo/odoo_8_ocb/src/OCA/OCB/openerp/http.py", line 300, in checked_call
return self.endpoint(*a, **kw)
File "/opt/odoo/odoo_8_ocb/src/OCA/OCB/openerp/http.py", line 796, in __call__
return self.method(*args, **kw)
File "/opt/odoo/odoo_8_ocb/src/OCA/OCB/openerp/http.py", line 396, in response_wrap
response = f(*args, **kw)
File "/opt/odoo/odoo_8_ocb/src/linked-addons/web/controllers/main.py", line 953, in call_button
action = self._call_kw(model, method, args, {})
File "/opt/odoo/odoo_8_ocb/src/linked-addons/web/controllers/main.py", line 941, in _call_kw
return getattr(request.registry.get(model), method)(request.cr, request.uid, *args, **kwargs)
File "/opt/odoo/odoo_8_ocb/src/OCA/OCB/openerp/api.py", line 241, in wrapper
return old_api(self, *args, **kwargs)
File "/opt/odoo/odoo_8_ocb/src/linked-addons/base/ir/ir_mail_server.py", line 215, in test_smtp_connection
raise osv.except_osv(_("Connection Test Succeeded!"), _("Everything seems properly set up!"))
except_orm: (u'\xa1Prueba de conexi\xf3n realizada con \xe9xito!', u'\xa1Todo parece correctamente configurado!')