I forget what file it is but theres something you need to change on the server so that it knows to accept the new htaccess. Theres a particular file that you need to access as root to tell it to recognise htaccess for that particular site. Ive done it to my sites and cant remember what file it was. Sorry
If you dont change the file, any htaccess will make a site unreadable until that htaccess is removed
# You may place any other directories or locations you wish to have
# access information for after this one.
You might see more or less sites listed. The site that you want the custom htaccess for will need to be added. You need everything from DIRECTORY to /DIRECTORY. Basically just copy whats there by adding another site#