Get 'Forbidden' error!

Hi,

We get 'Forbidden' error when we try to update a post/page. Tried creating a new page and it works and the same cannot be edited. ; ( could this be a DB issue?
Everything was working fine couple of days back.

Error is:
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Forbidden

You don't have permission to access /wp-admin/post.php on this server.
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We are using WordPress(MultiSite) 3.1.2 with MultiDB.