Permalink and subfolder issue

All my wordpress sites use the permalink parameter post-name I think, which means if the site name is “abc” then it will b:
mysite.com/abc
However for a program I need to create a subfolder which shall look like this:
mysite.com/abc/def/file.rar or
mysite.com/abc/file.rar

The problem is following: as soon I create a subfolder “abc” WordPress cannot display the WP page mysite.com/abc (404 – Error not found)

Does anyone have any idea of how I can create this subfolder abc in a way that it will also display the WP page mysite.com/abc ?

I found 1 article about it, but not sure if it´s explained here as they used another subfolder name, I really need the same subfolder name:
http://wordpress.stackexchange.com/questions/6373/wp-page-and-subdirectory-with-same-name

Kind regards, Test5000