Several users can't send encrypted messages in Exchange from Outlook, however they can do it from OWA, also they can send encrypted messages if recipient send them signed mail first (as for recipients outside organization).
The error is "Microsoft Office Outlook had problems encrypting this message because following recipients had missing or invalid certificates, or conflicting or unsupported encryption capabilities."
Other users can send encrypted messages to all recipients inside organization.
Outlook configured for cached exchange mode (same as for other users where all works) and it seems that downloading OAB works without problems. Certifiacte is from local authority and is valid and active in encryption settings, all other settings are defaults.
How can i check that Outlook have recipient's certificate in address book?