Failure when using existing tag and running under UWSGI

[floria...@gmail.com]

Dear all of you,
I have read a lot around and can't find an answer.
I get a strange behaviour with taggit (used in cab application, what runs djangosnippets, that I have installed on my personnal server).

When I create a tag it is working well.
However if I want to reuse an existing tag for my snippet, when I try to save the form, it is failing.

The fact here is that the message is simply nginx error occured, nothing anywhere in log neither nginx, uwsgi emperor, uwsgi vassal, in debug mode, no debug page.
I've tried to run the same into runserver_plus, the save works normally.

Have you any idea to help me investigate this, or any reference to give me?

Thank you.