Have you tried:
– deactivating all plugins to see if this resolves the problem? If this works, re-activate the plugins one by one until you find the problematic plugin(s).
– switching to the default theme to rule out any theme-specific problems?
– resetting the plugins folder by FTP or phpMyAdmin? Sometimes, an apparently inactive plugin can still cause problems.
I did it, but this didn’t solve the problem.
The problem resolution is like that explained in this post:
http://wordpress.org/support/topic/420642?replies=7
there was a
‘id’ => ‘sidebar-$i’
in the functions.php file inside
function my_register_sidebar()
(inside parameter array)
this was the source of the problem: removing that line is the solution for my topic!
Thanks for your help.