Try checking your file permissions?
Basically our editor (like Joomla) needs folders and files to be read / writable and at the entry file (this being the files which your web browsers need execute) may also be read / write and executable. Maybe this could be why it is working all your other sites and not on this particular one?
Joomla recommend 755 and 0644 for folders and files respectively with suPHP installed running on PHP & MySQL 5+ which gives developers like us a level playing field to work too. However, you may be using a different configuration and may need to use 777 for your files. Then again some configurations will not permit you to use 777 (which could be your problem)!
How to perform quick diagnostic test
You can check to see if this is happening by installing Firebug (which is a free 3rd party extensions for Firefox - addons.mozilla.org/en-US/firefox/addon/1843/ ). Once installed you can open up Firebug > Enabled the ‘Console’ Tab, visit the page where the error is occurring. If it reports:
files are not loaded... / 500 internal server error.../ file permission restrictions...etc
or something similar it is likely to be a server side file permission issue.
What should I do?
I would recommend contacting your hosting provider and ask them what the correct permission should be for your server? Some may make the change for you, if not then, you will have to use an FTP program and login to the location of your Joomla site and change permissions directly on the server. Alternatively, if you are a Business & Commercial subscriber we will be happy to make the change for you.
For more official documentation on Joomla’s hosting requirements, please see below:
If this is not the case, can you tell me a bit more about your configuration?
(1.) Joomla! version,
(2.) Server type,
(4.) Also would you be able to provide us with a screenshot of problem?
(5.) At this point we will really need an error report?
To do this you could use Firebug (which is a extensions for Firefox - addons.mozilla.org/en-US/firefox/addon/1843/ ). Once installed would you: 1.) open up Firebug > 2.) Enabled the ‘Console’ Tab, 3.) visit the page where the error is occurring and 4.) paste the ‘error report’ when you received the error.