If you have found that are getting the Joomla  "You are not authorised to view this resource" message on news or other similar items when your site appears to be working in all other respects then try this sequence of changes - it might just help.

Access levels as they should be - Public

Check whether the access level to see whether the offending items should show for all users or only for users with privilege.

If your item is a news item then  If your item generates the error when using the latest, most popular or similar modules then check to see if the item appears in the normal blog or news pages.

This will give you an idea as to when the problem occurs and should help to point you toward a possible solution.

This error occurred on one of my sites when I installed a latest news module which showed a valid link to the news item. However, when I clicked on the offending news item link I received the dreaded "You are not authorised to view this resource" message. This occured a lot when creating new news items. In this particular case the news items appear in the BLOG but are not reachable via the latest items module.

These are the things that each suffering news item appeared to have in common:

• The names of the news items were long
• The news names often contained a non-text character such as !
• The news items had a name but no alias title

To get round this I have tried a lot of different fixes but in the end I have a solution, of sorts, that works for me:

• If Artio JoomSEF or similar SEF tool is installed and enabled - then clear the SEF cache
• If you have 3rd party cache tools like Pagecache installed then be sure to turn off the default Joomla cacheing, it is not necessary to have both.
• If you have a 3rd party cache tool installed then temporarily disable the cache component.

turn off the default Joomla cache

• 

  Is there an alias for the article?
  Shorten the news item name and remove any non-alpha numeric characters
• Ensure that the offending items have suitable aliases in place, not too long, no non-alpha numeric characters 
• clear the 3rd party caches

These modifications often fix the problem but if the problem still persists I do the following:

A news item can have intro text and main text. I always make sure there is some text in both text areas, this causes a "read more" link to appear on the BLOG page. For some unknown reason this appears to be beneficial to reducing the occurrence of this error. I don't know why.

Finally if it still occurs then you need to copy the content from the offending article and create a new article of the same name, remember to unpublish the old.
When the article appears as it should, turn the page cacheing back on.

This worked for the old  "You are not authorised to view this resource" error message encountered on Joomla 1.0.