create a measure of latest date in a column

I want to put a tile on my report carrying the latest date in the data used.

I've tried several ways:

1: Measure = LASTDATE(my_table[Date])

Result: no error, blank visual

2: Measure = LASTDATE(DISTINCT(my_table[DateTime]))

Result: MdxScript(Model) (1, 46) Calculation error in measure 'gen_edi_stats_addl'[Measure]: A date column containing duplicate dates was specified in the call to function 'LASTDATE'. This is not supported.

3: Measure = LASTDATE(DISTINCT(my_table[DateTime]))

Result: Still the same as 2.

Any idea? Thanks!