vB 4.1.1 403 error

[Morpheus NS]

Hello, everyone. I have a problem with my forum. It started suddenly, and I don't know what could cause it. I didn't find an answer using search option.

On certain threads, when user clicks on a page number next to the name of the topic, he/she gets this error:

Forbidden

You don't have permission to access /showthread.php/390-Dobra-utakmica-ili......./page3 on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.
Apache mod_fcgid/2.3.6 mod_auth_passthrough/2.1 mod_bwlimited/1.4 FrontPage/5.0.2.2635 Server at nsportal.info Port 80

If user clicks on "the last unread post" link, he gets to the last page of the thread, but cannot see any of the previous pages. Is this a server error or is something wrong in vbulletin?

This does not happen on all the threads with more than one page, only on certain threads.

Edit:

I sorted it out. I changed my Friendly URL settings. I was using "Advanced Friendly URLs". After I switched back to "Standard URLs", everything is ok.