Convert.subString stopped working

Hi,

For some reason this piece of code has stopped worked:

var date = APPLICATION.getInfo().dateNowInternalFormat;

currentYear = Convert.subString(date, 0, 4);

currentMonth = Convert.subString(date, 4, 6);

This is the error message I get for the rows that starts with currentYear and currentMonth:

Couldn´t resolve reference to Member 'subString'

Couldn´t resolve reference to Variable 'Convert'

Any idea what I´m missing?

Thanks,

Anders