Ezinearticles duplicate article error

I'm trying this spinning software to write articles.. And then submit them to ezine.. But I get this error:

Thank you for your submission to EzineArticles.com titled "*******".
Unfortunately, our system has identified your article as being the same, similar or contains parts the same as one of your existing articles.

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How unique must an article be to avoid being detected by their system like that? The articles I submitted was about 10% unique accoring to this tool:
http://www.dupecop.com/duplicate-content-checker.php