Hi,
thank you very much for the clarification.
I found "Single Sign-In for Domains" plugin, which solves this.

Thanks once again.

I have multilingual web with Joomla 2.5.14 and JoomSEF 4.5.1 on separate domains (.com and .cz).
All works fine for public users.
When an registered user logins on one domain (e.g. com), all features for registered users are available. When this user switch to another language (domain .cz), it is only guest and all contents for registered user is hidden. If the same user login first on domain .cz, contents for registered is available, after switching to english (.com), registered user contents is again hidden.
I don't know, whether this is due Joomla or JoomSEF.
For reasons shared content between languages i need to be login valid in both languages.

Anyone have any idea please?