Hi Darko,
you can try this code:
void deleteRow()
{
Worksheet wks = Project.ActiveLayer();
if(NULL==wks)
return; // no active window, or not a worksheet
int rowNumber, rowCount, firstCol;
rowNumber = wks.GetNumCols(); //number of rows in aktive worksheet
rowCount = 3; // for every third "rowCount = 3" and so on
firstCol = 0; // the first row to delete
int jj = 0;
for( int ii = 1; ii <= ((rowNumber - firstCol + rowCount) / rowCount); ii++ )
{
wks.DeleteCol(firstCol + jj);
jj=jj+rowCount - 1;
}
}