[RBG7-L] - UNION

[ELOEN]

The command:

SEL NATPloiaKvd,MAX(NATPloiaOnoma)+
  FROM TNATYphr WHERE INT(NATPloiaKvd) > 0 GROUP BY NATPloiaKvd+
  UNION+
  SEL MAX(NATPloiaKvd),NATPloiaOnoma FROM TNATYphr WHERE+
  INT(NATPloiaKvd) = 0 GROUP BY NATPloiaOnoma

Gives:
-ERROR- Column type mismatch in UNION (2372)

Anyone knows why?

TIA
Polychronis