DB problem ?

Hi,

I wanted to ask if someone can help me with this problem I′m having.
First of all i wanted to send the link of my blog, so you can see the problem inmediatelly.

https://www.wikichaves.com/blog/

I′m having this error message:
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Warning: array_keys() [function.array-keys]: The first argument should be an array in /home/rv000048/public_html/blog/wp-includes/widgets.php on line 686

Warning: Invalid argument supplied for foreach() in /home/rv000048/public_html/blog/wp-includes/widgets.php on line 686
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I′ve tried reinstalling WP and updating it, but the problem remains. I think there is some DB problem, but the weird thing is that i haven′t changed anything on it.

Can anybody help me ?

Thanks !

Francisco