Ever heard of a subdirectory being penalized in Google ?

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Sorry, this is a repeat post from the General Forum. I didn’t realize that it should have been placed in this forum. Apologies for the duplication.
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OK guys, I know this board is not really an SEO board, but I wanted to throw out a question to all. Without spamming my domain name to you guys, I own a domain, since 1997, and have been active with Affiliate programs since the beginning of the year. I have created 6 websites under this domain, each of which is totally independent. Hence, my website structure is:

http://www.domain.com/subdir1/name.htm
http://www.domain.com/subdir2/name.htm
.
.
.
http://www.domain.com/subdir6/name.htm

5 of my 6 websites have decent ranking in the SE’s, including my Poker site (thankfully !). The one site that doesn’t show up anywhere for any of my keywords, in Google, is my Casino site. It show’s up in Google only if I type in the full URL into Google’s search box. Hence, it hasn’t been banished. The site has a PR of 4, and is referenced by all my other sites. The screen layout of the site mimics my other 5 sites, but the content is different.

It never shows up in Google for any of my Keywords. Has anyone ever heard of a “subdirectory” website, as described above, being penalized ? It is definitely not a sandbox issue, since the domain has existed since 1997, and I created this website back in May of this year.

Anybody have any thoughts on this at all ?

Thanks in advance,

Doug