Connecting Fiber interfaces on Cisco switches

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http://serverfault.com – I'm trying to replace an old Cisco Catalyst 2950 with a new Cisco 3750X. Unfortunately, these SFP's are so expensive, I'm trying to work with what I've got. Please note the diagram to see what connections I have. The core switch is SX, as is the old switch it was running to. When I hook a cable [had to be a different end connector to fit the new SFP, so it's really a different cable but attached to the same patch port] to the new switch, nothing happens and it reports the line is down [Physical Layer error]. This port reports that it is a 1000BaseLX, which from what I understand is Single (HowTos)