Tuaris and Haudini,
after I installed the older firmware and replaced the ethernet cable, the message "socket Connect failed" also appeared. However, after 2 or 3 minutes it disappeared and my S9 connected to the pools. I have NiceHash as my 1st pool, and slush as my 2nd pool.
Haudini,
Antminer-S9-all-201705031838-650M-user-Update2UBI-NF.tar.gz worked for me. I tried all the others and none worked.