change polygon pattern style by code

[Anonymous]

Hi, I have a problem to change the pattern style of a polygon with Autocad 2007 using Object ARX.
I use this code (that worked in Autocad 2006):

AcDbMPolygon *pPol= NULL;
(... I put in pPol my entity polygon)
pPol->setPattern(AcDbHatch::kPreDefined,"SOLID");
pPol->ev aluateHatch(false);

When I use setPattern it give me the error Acad::eInvalidInput. What is wrong?
thanks, Micaela