I found the reason. It was a nasty problem from ours. My team have merged all Castle ActiveRecord related assemblies together with ilmerge.exe and suppose named it Company.NHibernate.dll. I have not merged NHibernate.Caches.SysCache.dll with Company.NHibernate.dll. I have just put NHibernate.Caches.SysCache.dll alongside of Company.NHibernate.dll and mentioned name of NHibernate.Caches.SysCache in provider_class.
When I merged NHibernate.Caches.SysCache.dll with Company.NHibernate.dll and mentioned name of Company.NHibernate.dll in provider_class instead, everything went OK.
Thanks all users that tried to help me.