Left Join - field not found

[dpstanley_13]

I have hit a wall and need another set of eyes on this.  I don't know why I am getting the "Field not found" error.

DateRangeBridge:
LOAD Distinct
Num(Date#(MeasureMonthDTS, 'YYYY-MM-DD')) & Num(Date#(MeasureMonthEndDTS, 'YYYY-MM-DD')) AS BridgeKey
,MeasureMonthDTS
,MeasureMonthEndDTS

Resident Fact;

Left Join (DateRangeBridge)

LOAD DateDT
Resident Calendar
Where Date(DateDT) >= Date(MeasureMonthDTS) and Date(DateDT) <= Date(MeasureMonthEndDTS);

Field 'MeasureMonthDTS' not found