Access Stats - Access Denied error

I've changed and uploaded the .pl scripts (755) and the logfiles folder (777) - however, I get an Access Denied message in my browser when I try and check the script.
Any ideas where I should be looking to correct the error.
(I've set it up on another site which did the same, until I moved the javascript between the </html> and <body> tags, and then it worked, but moving this one doesn't correct the problem.)

Many thanks