DSC 4x4 Inactive Brake - Wheel Speed Sensor?

[StartX5]

Hi everyone -
While heading to work this morning, i merged onto highway for 500 feets, i received a warning message on dash: "DSC 4x4 inactive" then after i applied on brake pedal DSC 4x4 inactive message was off but there is a yellow BRAKE light came one with 4x4 triangle light on.


I am thinking about the wheel speed senor fail in this.
Is this message indicate wheel speed sensor or brake sensor? I replaced (DIY) all new brake rotors, pads and sensor in Octorber- 2011 + brake fluid change without an issue.

Is it safe to drive with 4x4 and yellow BRAKE light is on for few days?

I haven't got a chance to scan the code because the scan tool is at home.

If wheel speed sensor fail, is that possible to replace speed sensor without undoing the wheel?