500 Internal Server Error - Please Help!

I followed the tutorial:
http://www.kirupa.com/web/custom404.htm to create custom 404 error pages. After uploading a file called .HTACCESS into the /www folder, my website began showing a 500 Internal Server Error page whenever I or other users went onto: [url=“http://www.excaliburfilmproductions.co.uk/”]http://www.excaliburfilmproductions.co.uk and any documents on that domain. However my subdomains remained unaffected by the problem. To resolve the problem I decided the goto the Easy Space control panel and sort out the problem in the DNS section. I deleted the www zone file and then created a new one. However, this did not solve the problem! I have no idea what to do next. Please help me resolve this problem. Thank you.