I want to use PHP as a extension.
So I changed as below.
# The extension to use for non index files:
$build_extension = ".php";

It works well in the normal index and non index files.

But after the "Login", I got a problem.
In the templetes, we use <%next_span%> code to go next or previous page.
This code make like this
"Page: 1 2 [>>]"

And I pressed "2", but I got this type of message.
"We don't seem to have a category by the name '3/4/7/more2.php"

So I changed the extension "shtml', It works well.
Why ?
After the Login, I can't go next page when I use "PHP' as a extension.