vlc on "Cannot enable seo_locale"

I'd like to enable the "seo_locale" plugin on my ZP 1.4.12 installation, but I cannot as "This plugin is not compatible with the dynamic locale Use subdomains option".

As far as I understood the "Use subdomains" option must be disabled in the "dynamic locale" plugin (it is). I also tried enabling "Use subdomains", but the problem persists.

Is there anything else I'm supposed to to to enable "seo_locale"?

Thanks a lot in advance,
Christoph