Explicit conversion from data type date to bigint is not allowed

This used to work with a column type of DATEIME but now it won't with DATE.

CONVERT(BIGINT,ev.StartDate) * -1

Is there anyway to get a BIGINT value from a DATE column?

Yet another option. This will even flip the sign for you

Example

Declare @YourTable table (StartDate date)
Insert Into @YourTable values ('2017-05-30')

Select DateDiff(DAY,StartDate,-1)
 From @YourTable

Returns

-42884