Pages with duplicate title tags in Wordpress MU

Checking in WMT I found several "pages with duplicate title tags".


example:

/mmofps/category/preview/
/mmorpg/category/preview/
/mmorts/category/preview/

As you can see I have created three sub-folders for each type of "online game": MMOFPS, MMORPG, and MMORTS. For each sub-folder (created with WP MU) I have the exact same categories, such as reviews, previews and guides.



This causes the problem of duplicate title tags. I would like to solve the problem and to do so I added a word to each category, transforming them into:

/mmofps/category/preview-mmofps/
/mmorpg/category/preview-mmorpg/
/mmorts/category/preview-mmorts/



In this way, however, I find many categories similar within each site. Example categories:

previews mmorpg
reviews mmorpg
guides mmorpg
interviews mmorpg
etc...

Repeat the word MMORPG in any category can be a problem? E 'a repetition harmful or considered as a kind of over-optimization? I think it's obvious that I'm looking for a solution to remove the duplicate tag without having to prevent indexing of categories, because they are very useful for SEO purposes.



Thanks to all who will help me.