Hi csoreto,
c is for carlos? cassanova maybe?
no worries i even get lost in that code
In function get_list_from_db (the one in sc_ajax_select_boxes class) around line 273 there is a line
$cmd = "SELECT $key_fld, $text_fld FROM $table ";
there you should add the distinct clause and make it like
$cmd = "SELECT DISTINCT $key_fld, $text_fld FROM $table ";
and it should do the trick.
Best regards
Panos