This thread is resolved. Here is a description of the problem and solution.
Problem: An error appears during the update process.
Solution: A reason can be an invalid site key and site URL.
Here's an outline of steps which help in the most of cases:
1. Generate a new site key (http://wpml.org/faq/install-wpml/)
2. Unregister WPML from your site. You can do this by clicking the Unregister button in Plugins >> Add New and navigate to "Commercial" section.
3. Register the site again from that place.
4. Finally, go to Dashboard >> Updates, choose WPML plugins for update and click on the update button.
Here's a video, which shows you the steps above: http://screencast.com/t/59yTtuGTGFF
Leave a comment in this thread, if you still have the error "PCLZIP_ERR_BAD_FORMAT (-10) : Unable to find End of Central Dir Record signature".
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