I'm using the plugin All in One SEO Pack and I've realised that if my post has a tag with something surrounded by quotation marks, as the tags go to the keywords meta, it doesn't validate HTML.
Example:
<meta name="keywords" content="name of tag1, name of tag2 with something surrounded by "quotation" marks" />
To fix this problem I've just removed the quotation marks adding this replace statement in line 329 of the aioseop.class.php file (version 1.6.8.2):
$keywords = str_replace('"','',$keywords);
Is there any other better solution?