You are trying to pass the list of holidays as a single parameter. The Networkdays() function will only allow multiple holidays to be passed as multiple parameters.

There is a way around this by using the Evaluate() function however. Like this:

holidayTable:

LOAD * INLINE [

Depot In;Depot Out;HL

1.5.2018; 31.5.2018;'1.5.2018','17.5.2018'

1.12.2017; 31.12.2017;'24.12.2018','25.12.2017','26.12.2017','31.12.2017'

] (delimiter is ';', no quotes);

D2:

NOCONCATENATE LOAD

  [Depot In],

  [Depot Out],

  Evaluate('Networkdays('&Chr(39)&[Depot In]&Chr(39)&','&Chr(39)&[Depot Out]&Chr(39)&','&HL&')') AS NWD

RESIDENT

  holidayTable;

DROP TABLE holidayTable;