hi Pavlo,
can you check for the server name provided in the RFC destinations like Virtual or physical host and also check the ssh known_known hosts file on target server.
also have you maitained the gatweway host and the gateway port correctly in RFC destination.
and does the SID of Gateway is different that your actual instance.
Check note http://service.sap.com/sap/support/notes/980266.
and try to connect from your CI to DB using ssh and see if it works without password. Due to the issue in os authentication it fails.
Let us know if this help.
Regards,
Ram