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It's not valid code because it includes a block element (the table) inside an inline element (the anchor tag). W3C Reference [w3.org]
Not valid doesn't mean that it can't work -- so I tested some browsers. The only browser where it worked was Opera. You're going to need to rethink this area of your page.
To do the same with ordinary HTML you have to put an anchor tag around the entire contents of each and every cell (use CSS to remove underlining if you wish) and it would not allow clicking on the table borders to count.
Ammon Johns