While trying to install WordPress MU in a subdirectory, you may come across an error:
There doesn’t seem to be a
wp-config.phpfile. I need this before we can get started.
I did come across it. There is a button: Create a Configuration File, I clicked on it, but nothing happened.
After some research I found that this exact problem happens because I had one WordPress install in an upper directory, that means: one more wp-config.php file.
I renamed that existing wp-config.php file – WordPress MU installation script was able to continue work. More information about standard installation can be found in wordpress.org codex: codex.wordpress.org/
After the installation is complete, you can rename wp-config.php file back. It won’t interfere with anything.