You're not getting the second line? How are you determining this?
With the usual lcd units, the first and second lines are not sequential so once you go past the 16th char on the first line, it won't go to the second line. for the first line, the command to locate the cursor is 0x80 + offset, for the second line the command is 0xc0 + offset. The following code copes with a 4 line display. I would suggest you read the relevant datasheet that explains all of this.

//----------------------------------------------------------------------------
//
//  Locate the lcd cursor. cursor position (0..max) in pos
// eg: for a 16 char * 2 display :- 0..15 is the top line, 16..31 is the bottom line
//
//----------------------------------------------------------------------------
void locate_cursor(char pos)
{
char a;

  a = pos % NUM_CH_LINE;
  switch(pos / NUM_CH_LINE)
    {
    case 0:
        lcd_comm_wr(a + 0x80);
        break;
    case 1:
        lcd_comm_wr(a + 0xc0);
        break;
    case 2:
        lcd_comm_wr(a + 0x94);
        break;
    case 3:
        lcd_comm_wr(a + 0xd4);
        break;
    }  
}