Despite the fact that our title has been approved, I can not find it and add it to my list

This sounds like you are using the old (7+ years out of date) version of IMDb.  

Please go to your site settings at https://secure.imdb.com/register-imdb/siteprefs and ensure both "Always display full cast and crew credits" and "Show reference view (old title/name page layout)" are unchecked.   These options are only for people who do not want to use IMDb's latest design and features; data on them runs 24-36 hours behind the rest of IMDb so they are not recommended for general use.  

I went to this page, but there all the settings are correct.

Please post the URL of the page which is generating a 404 error.

This page loads fine here sorry, as does its only title @ http://www.imdb.com/title/tt7745106/ 

and why is this happening ??

Please post a screen-grab of the 404 page with the URL visible and we can take another look. 

can this problem be due to the fact that my profile is not being searched for in search results?

Please see our advice above.  The only way to get to that page when you click on a title is if your settings are wrong ...

Please go to your site settings at https://secure.imdb.com/register-imdb/siteprefs and ensure both "Always display full cast and crew credits" and "Show reference view (old title/name page layout)" are unchecked.

Please look at those again and then visit http://www.imdb.com/title/tt7745106/ 

Thank you very much!! All is adjusted !!