[Koha] connecting to zs39

Hi, I have Koha running on an Linux server running Ubuntu 12.04 Koha runs fine - no issues. I have been trying to connect to it via ZS39 but unable to connect. Yaz client gives me this error = System (lower-layer) error Help/ideas would be appreciated. -- Solomon Mwangi Cell:+254 715 502349 Skype: solomon.mwangi