I downloaded latest 2.0 Omega theme and uploaded to the server.
The Osclass back office themes menu shows the theme as inactive.
After clicking ACTIVATE button on the OMEGA theme thumbnail the blank screen appear with this error:


Fatal error: Cannot redeclare check_plugins_admin_footer() (previously declared in /public_html/oc-admin/themes/omega/functions.php:462) in /public_html/oc-content/themes/omega/functions.php on line 465

Do you run it on osclass 4.0?

Yes 4.0

Also the free PLUGINS UPDATER plugin shows the OMEGA theme as version v1.1.0 but inactive (but v2.0 is uploaded to the server)

@piter
in osclass v4.0, omega theme comes as default so no action is required.
But what you've done is that you have added Omega as front-office theme that is evident from this part of error:
/public_html/oc-content/themes/

Yes, it was my mistake. I uploaded it to both oc-admin and oc-content folders.

Just to let you know that even when ver OMEGA 2.0 is uploaded and active via Admin Themes Plugin, your UPDATER plugin shows incorrect information (no version, not downloaded)

Right because ocadmin themes were not integrated into this plugin yet.