If you can confirm, that the drive itself is working properly, try plugging it in, after the Camera is fully booted (Had Problems with both HDMI and Ethernet when something was plugged in before the Camera was booted, so i would not be Surprised, if something similar could happen with eSATA. Had no issues with that myself so far, but you can never know).
If that still does not work, i would try replacing that Cable, maybe that is broken (unless you have a way to test that, and make sure it works, like an PC that has a eSATAp Port somewhere to plug it in and Check).