Error 403 .htaccess and misplaced files..

Hi,

I am in the process of building a WordPress (as CMS) bespoke site for a client, my first attempt at using WordPress like this.

I have come across the error:
Error 403 – Forbidden

You tried to access a document for which you don’t have privileges.

My site has been running fine until this morning when I dropped a new index.php file to the root directory:
/BlackRat

When it should have gone into:
/BlackRat/wp-content/themes/BLANK-Theme

When I got a fatal error after refreshing my browser:
Fatal error: Call to undefined function get_header()

I googled it, looked back, realised my mistake and deleted the index.php from /Blackrat, refreshed and got the 403 error.

Im struggling to find anyone with the same problem and coming across lots of posts about the .htaccess file, none of them very relevant.

My .htaccess looks like this:
AddType x-mapp-php5 .php
# BEGIN WordPress

# END WordPress

I updated the file with php5 recently to run a certain plug in, everything was working fine and I have not added any plug ins since.

Ive tried changing file permissions, creating a fresh .htacess and adding it to subdirectories (it was initially only in /Blackrat) and replacing all theme files. All other sites on hosted by me are unaffected, including another wordpress site. No joy.

Any help or pointers is much appreciated, thanks,

Dooby