Funny thing.
In mine, it works...
On mine, If I subtract one date from the other I get the number of days in between...which is another integer, I guess. and '%' is the modular operator. Doesnt it work like this on yours?
If I substract one date from the other I get an interval.
Which version are you using?
I am using 7.4.12 version of postgres.
try
SELECT (date - '2007-01-01') % 2
FROM table
to see if you get zeroes and ones .
It's not working. I've got the same error.