duplicate folder

I have an error on my blog after install MU.

My principal blog is installed into http://www.legiondemarketing.com/blog

My blog works ok until i configure it for MU, now when i choose any section the "/blog" folder was duplicated, like:

http://www.legiondemarketing.com/blog/blog/category/noticias/

you can see /blog appears two times.

The same occurs with post.
I can read the posts anyway but i can't see the categories.

How can i solve this?

Maybe this issue was caused because i have a redirection on my primary domain to the "/blog" folder?