Anche io stesso problema:

08:42:59] "GET /seedoo/etichetta/20250000005.pdf HTTP/1.1" 500 -
2025-09-14 08:42:59,862 11525 ERROR protocollo-pb werkzeug: Error on request:
Traceback (most recent call last):
  File "/home/emmecoop_consulting/seedoo/venv/lib/python2.7/site-packages/werkzeug/serving.py", line 177, in run_wsgi
    execute(self.server.app)
  File "/home/emmecoop_consulting/seedoo/venv/lib/python2.7/site-packages/werkzeug/serving.py", line 165, in execute
    application_iter = app(environ, start_response)
  File "/home/emmecoop_consulting/seedoo/OCB/openerp/service/server.py", line 294, in app
    return self.app(e, s)
  File "/home/emmecoop_consulting/seedoo/OCB/openerp/service/wsgi_server.py", line 216, in application
    return application_unproxied(environ, start_response)
  File "/home/emmecoop_consulting/seedoo/OCB/openerp/service/wsgi_server.py", line 202, in application_unproxied
    result = handler(environ, start_response)
  File "/home/emmecoop_consulting/seedoo/OCB/openerp/http.py", line 1299, in __call__
    return self.dispatch(environ, start_response)
  File "/home/emmecoop_consulting/seedoo/OCB/openerp/http.py", line 1273, in __call__
    return self.app(environ, start_wrapped)
  File "/home/emmecoop_consulting/seedoo/venv/lib/python2.7/site-packages/werkzeug/wsgi.py", line 588, in __call__
    return self.app(environ, start_response)
  File "/home/emmecoop_consulting/seedoo/OCB/openerp/http.py", line 1273, in __call__
    return self.app(environ, start_wrapped)
  File "/home/emmecoop_consulting/seedoo/venv/lib/python2.7/site-packages/werkzeug/wsgi.py", line 588, in __call__
    return self.app(environ, start_response)
  File "/home/emmecoop_consulting/seedoo/OCB/openerp/http.py", line 1273, in __call__
    return self.app(environ, start_wrapped)
  File "/home/emmecoop_consulting/seedoo/venv/lib/python2.7/site-packages/werkzeug/wsgi.py", line 588, in __call__
    return self.app(environ, start_response)
  File "/home/emmecoop_consulting/seedoo/OCB/openerp/http.py", line 1273, in __call__
    return self.app(environ, start_wrapped)
  File "/home/emmecoop_consulting/seedoo/venv/lib/python2.7/site-packages/werkzeug/wsgi.py", line 588, in __call__
    return self.app(environ, start_response)
  File "/home/emmecoop_consulting/seedoo/OCB/openerp/http.py", line 1273, in __call__
    return self.app(environ, start_wrapped)
  File "/home/emmecoop_consulting/seedoo/venv/lib/python2.7/site-packages/werkzeug/wsgi.py", line 588, in __call__
    return self.app(environ, start_response)
  File "/home/emmecoop_consulting/seedoo/OCB/openerp/http.py", line 1453, in dispatch
    result = ir_http._dispatch()
  File "/home/emmecoop_consulting/seedoo/OCB/openerp/addons/base/ir/ir_http.py", line 175, in _dispatch
    return self._handle_exception(e)
  File "/home/emmecoop_consulting/seedoo/OCB/openerp/addons/base/ir/ir_http.py", line 145, in _handle_exception
    return request._handle_exception(exception)
  File "/home/emmecoop_consulting/seedoo/OCB/openerp/http.py", line 675, in _handle_exception
    return super(HttpRequest, self)._handle_exception(exception)
  File "/home/emmecoop_consulting/seedoo/OCB/openerp/addons/base/ir/ir_http.py", line 171, in _dispatch
    result = request.dispatch()
  File "/home/emmecoop_consulting/seedoo/OCB/openerp/http.py", line 693, in dispatch
    r = self._call_function(**self.params)
  File "/home/emmecoop_consulting/seedoo/OCB/openerp/http.py", line 319, in _call_function
    return checked_call(self.db, *args, **kwargs)
  File "/home/emmecoop_consulting/seedoo/OCB/openerp/service/model.py", line 118, in wrapper
    return f(dbname, *args, **kwargs)
  File "/home/emmecoop_consulting/seedoo/OCB/openerp/http.py", line 316, in checked_call
    return self.endpoint(*a, **kw)
  File "/home/emmecoop_consulting/seedoo/OCB/openerp/http.py", line 812, in __call__
    return self.method(*args, **kw)
  File "/home/emmecoop_consulting/seedoo/OCB/openerp/http.py", line 412, in response_wrap
    response = f(*args, **kw)
  File "/home/emmecoop_consulting/seedoo/seedoo-core/seedoo_protocollo_dematerializzazione/controller/etichetta.py", line 192, in etichetta
    company_logo.paste(company_logo_png, (0, 0), company_logo_png)
  File "/home/emmecoop_consulting/seedoo/venv/lib/python2.7/site-packages/PIL/Image.py", line 1335, in paste
    self.im.paste(im, box, mask.im)
ValueError: bad transparency mask

2018-10-24 09:46:32,276 1928 INFO seedoo werkzeug: - - [24/Oct/2018 09:46:32] "GET /seedoo/etichetta/3 HTTP/1.1" 500 -

Ciao Pasquale,
l'errore 500 un errore interno del server Odoo che potrebbe essere causato da diversi fattori.
Per risolvere il problema è fondamentale capire il punto esatto del codice dove si è verificato l'errore.
Servirebbe quindi il Traceback del problema.
Odoo ha un file di log che, se hai seguito la guida, puoi trovare nella HOME dell'utente chiamato "seedoo.log".

Potresti riportare qui sul forum tutta la parte relativa all'errore?

Se non dovessi riuscire a trovarlo, prova ad effettuare di nuovo l'operazione di Stampa Etichetta.
L'errore dovrebbe ripetersi e dovresti trovare la parte interessata alla fine del file.

Sarebbe utile, inoltre, sapere quale versione/commit stai usando, o più o meno il giorno in cui hai preso il codice, per essere sicuri che il problema non sia dovuto a vecchie versioni e non sia già stato risolto.