I've tested it in several scenes (even with a default blender scene) and I always get just the same result: if I try to render the Z-depth image (Kernel type: Info-channel > Z-Depth) in Blender Octane Edition I get plain white image. At the sme time when I use "Rendered" Viewport Shading Z-Depth image looks fine. It seems like "Z-Depth max" parameter is being set to a value close to 0 during the render for some reason.
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A. OS Windows 7 with lastest updates at the current date
B. GTX 680 4Gb + GTX 770 4Gb
C. 24 Gb RAM
D. Nvidia GeForce Game Reay Driver 378.49
E. OctaneRender Standalone 3.05.2
F. OctaneRender plugin for Blender v2.25, OctaneServer v11.21
G. Blender 2.78a Octane Render edition