If it helps at all, I have the Canon mount version, and occasionally I get a "lens communication" error. If it happens, I normally switch off the camera, take the lens off and mount it again, and switch the camera on again clears it. I suspect the electrical contacts may be marginal at times, but overall it happens rarely for me. I don't get that with any other lens.
_________________Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.