Error 500 when to view the article


I have installed OPS last version. Everything is ok in the admin section, and I published several articles.
On frontpage, I view the titles of the articles with link to details, bit when I click on link I am directed to where I get a HTTP ERROR 500, This page isn’t working. is currently unable to handle this request.

In error.log I have ”PHP Warning: Trying to access array offset on value of type null in /home/r93046tele/preprints/plugins/themes/default/DefaultThemePlugin.php on line 188”

Also, in admin area, at Settings / Distribution / Access / Posting Mode , I have two options, ”The server will provide open access to its contents.” and ”OPS will not be used to post the server’s contents online.” None of them is selected and when I try to select first one I cannot save it (after refresh, I see none selected).

Is it possible to help me to overcome this prooblem?

Thank you,


I solved it, one of the plugin caused this error, Citation Style Language.