That was my best guess with so little information to go on. Like I said, my plug is able to scan that file just fine on my server, so it must be something about your server that is limiting my plugin or otherwise preventing that file from being read.
You can check the file permission in-place, or check your error_log file to see if there is a relevant error reported every time you scan that file. you could also check the results of the phpinfo() function to be sure that your php.ini file is affecting the appropriate values that you have set.
You may also want to inquire about your servers processor and memory capacity and other server limitation with your hosting provider. If this (or any other issue with your hosting) are a real problem for you and you would like to switch to a better host then I would be happy to move your site to one of my servers. I do offer Super Secure Hosting for $12/month per site if you are interested.