I also had the same problem last January in my '06 FEH. The dealer fix for it was to "Apply special grease to HPA connector on ACU and reprogram ABS module to latest calibration and perform air bleed ck". They also listed a "C1475 in ABS module" and referenced TSB 062201. I haven't had the problem since, but I also garage mine so I'm less likely to see it.

My 4WD
Wife's 4WD