Rules: Initialization of var DateTime fails; => How to solve?

I’m not a rules guru but try:

var DateTime Front_Bedroom_Motion_Detector_Last_Triggered = now as Number

Or

var DateTime Front_Bedroom_Motion_Detector_Last_Triggered = new DateTime(localLastMeasurement_00.state.toString).toString("yyMMddHHmm")

See also these topics for dates, times, and motion: