How to print DateTime variable in the RAISERROR method?

The supplied value must be a constant or a variable. You cannot specify a function name as a parameter value. (from MSDN Executing Stored Procedures).

You need to do something like this:

declare @EffectiveStartDateText varchar(30)
set @EffectiveStartDateText = cast(@EffectiveStartDate as varchar)

declare @EffectiveEndDateText varchar(30)
set @EffectiveEndDateText = cast(@EffectiveEndDate as varchar)

RAISERROR (
    'SPName: InsertUpdateLiquidityDateRule:  Start Date: %s cannot  be greater than End Date %s',
    11,
    1,
    @EffectiveStartDateText,
    @EffectiveEndDateText);