SSMS 32bit can't connect SSIS 64bit
Finaly got it working. Not quite sure of explanation, but I think it had something to do with Kerberos / NTLM authentication.

SSIS was running under domain account that was not registered with SPN. Changing to "Log On as Built-in Account" as Network Service and restarting SSIS service solved the problem.

But also I'm (almost) sure that I've tried it earlier when I found his thread: http://social.msdn.microsoft.com/Forums/en/sqlintegrationservices/thread/bba0d02d-67d0-42d4-af20-5ea8a4ae443b

Also these articles explaining Kerberos, NTLM and checking SPN settings were helpful:


http://sql-articles.com/articles/dba/linked-server-part-2/
http://blogs.msdn.com/b/sql_protocols/archive/2006/12/02/understanding-kerberos-and-ntlm-authentication-in-sql-server-connections.aspx