my Controller is not working

[eluser]nencor[/eluser]
i have some controller like this

Code:

<td colspan="8">&lt;?php
                echo form_open('c_kategorimaterial/addkategorimaterial');
                echo form_submit('tambah','tambah');                
                echo form_close();
                ?&gt;</td>

then i copy paste them, then change into similiar controller that open different form

Code:

<td colspan="7">&lt;?php
                echo form_open('C_material/addmaterial');
                echo form_submit('tambah','tambah');
                echo form_close();
                ?&gt;</td>

why does the second controller is not working ?

edit : it works when i use

Code:

<td colspan="7">
                    <a href='&lt;?php echo base_url(); ?&gt;index.php/c_material/addmaterial'>Tambah</a>
                </td>

why does the button is not working ?