Dear Friend,
Thanks for you help.
Actually after one of the re-installations there was a space character in the directory of this widget. It is now fixed and working.
Thank you very much!
Thanks a lot for your reply!
I tried the change with https:// but nothing has changed.
Actually, the rest of installed plugins are:
All in One SEO Pack, Category Posts Widget, Contact Form 7, Embed YouTube Videos in WordPress, File Gallery, qTranslate, Query Posts, WordPress Category Archive, WP Security Scan
Could you imagine of a conflict with one of those?
Thanks in advance