So,
I reinstall os class on an subdomain:

http://test.anuntbeton.ro/osclass/index.php?page=item&action=item_add

Fresh install, no other codes inserted or modify.... just image required plugin...but... don't work!!

@ifrim
You have old theme files.

http://forums.mb-themes.com/veronika-osclass-responsive-theme/updates-1156/

v1.1.8 (2017-05-04)
- fixed compatibility issues with Image Required plugin
Error it reference to was fixed in newer versions.

I downloaded today from your site

That is strange. I will reupload theme files today and will let you know.

Can u test on an subdomain pls?

@ifrim
Redownload theme and reupload theme files.

1. Can u pls test this before give to us?
2. You test your plugin on you themes before give to us?
3. This plugin image required don't work on this theme!

@ifrim
1) yes we do
2) yes we did
3) I must disagree:
https://plugins2.abprofitrade.eu/item/new

4) Can you listen to support and replace theme files?

OK!
After 3 re-uploads it works!
Thank you!

Now, one more question... how can i make one page like https://plugins2.abprofitrade.eu/item/new
for my website...  don't like very much that steps from my website...

Thank you!

@ifrim
https://plugins2.abprofitrade.eu/oc-content/themes/veronika/css/style.css

See first 3 lines.

@Frosticek

What file do I need to change to fix this problem?

or do you have to update the whole theme?

bad to update the theme all that miss a translation that does direct in the html code ...

@Leandro
That is why there exists po files and translations should be done in these files, not in php files.
It should be item-post.php, item-edit.php and functions.php