Original:

void nanny_get_new_race( DESCRIPTOR_DATA * d, const char *argument )
{
   char buf[MAX_STRING_LENGTH], arg[MAX_STRING_LENGTH], buf2[MAX_STRING_LENGTH];
   CHAR_DATA *ch = d->character;
   int iRace, iClass, col = 0;

   argument = one_argument( argument, arg );
   
   if( !str_cmp( arg, "help" ) )
   {
      do_help( ch, argument );
      send_to_desc_color( "&zPlease choose a race:&w ", d );
      return;
   }

   for( iRace = 0; iRace < MAX_RACE; iRace++ )
   {
      if( toupper( arg[0] ) == toupper( race_table[iRace].race_name[0] )
         && !str_prefix( arg, race_table[iRace].race_name ) )
      {
         ch->race = iRace;
         break;
      }
   }

   if( iRace == MAX_RACE || !race_table[iRace].race_name || race_table[iRace].race_name[0] == '\0' )
   {
      send_to_desc_color( "&zThat's not a race.\r\nWhat is your race?&w ", d );
      return;
   }

   send_to_desc_color( "\r\n&zPlease choose a main ability from the following classes:&w\r\n", d );
   
   buf[0] = '\0';
   col = 0;
   
   for( iClass = 0; iClass < MAX_ABILITY; iClass++ )
   {
      if( ability_name[iClass] && ability_name[iClass][0] != '\0' && str_cmp( ability_name[iClass], "force" ) )
      {
         snprintf( buf2, MAX_STRING_LENGTH, "&R[&z%-15.15s&R]&w  ", ability_name[iClass] );
         mudstrlcat( buf, buf2, MAX_STRING_LENGTH );
         if( ++col % 4 == 0 )
         {
            mudstrlcat( buf, "\r\n", MAX_STRING_LENGTH );
            send_to_desc_color( buf, d );
            buf[0] = '\0';
         }
      }
   }
   
   if( col % 4 != 0 )
      mudstrlcat( buf, "\r\n", MAX_STRING_LENGTH );
   mudstrlcat( buf, "&z:&w ", MAX_STRING_LENGTH );

   send_to_desc_color( buf, d );
   d->connected = CON_GET_NEW_CLASS;
}

Fix:

void nanny_get_new_race( DESCRIPTOR_DATA * d, const char *argument )
{
   char buf[MAX_STRING_LENGTH], arg[MAX_STRING_LENGTH], buf2[MAX_STRING_LENGTH];
   CHAR_DATA *ch = d->character;
   int iRace, iClass, col = 0;

   argument = one_argument( argument, arg );
   
   if( !str_cmp( arg, "help" ) )
   {
      do_help( ch, argument );
      send_to_desc_color( "&zPlease choose a race:&w ", d );
      return;
   }

    if( arg == NULL || arg[0] == '\0' )
    {
    send_to_desc_color("&zYou must enter a valid race name.\r\nWhat is your race?&w ", d);
    return;
    }

   for( iRace = 0; iRace < MAX_RACE; iRace++ )
   {
	   if( race_table[iRace].race_name == NULL || race_table[iRace].race_name[0] == '\0' )
    continue;

      if( toupper( arg[0] ) == toupper( race_table[iRace].race_name[0] )
         && !str_prefix( arg, race_table[iRace].race_name ) )
      {
         ch->race = iRace;
         break;
      }
   }

    if( iRace == MAX_RACE || !race_table[iRace].race_name || race_table[iRace].race_name[0] == '\0' )
   {
      send_to_desc_color( "&zThat's not a race.\r\nWhat is your race?&w ", d );
      return;
   }

   send_to_desc_color( "\r\n&zPlease choose a main ability from the following classes:&w\r\n", d );
   
   buf[0] = '\0';
   col = 0;
   
   for( iClass = 0; iClass < MAX_ABILITY; iClass++ )
   {
      if( ability_name[iClass] && ability_name[iClass][0] != '\0' && str_cmp( ability_name[iClass], "force" ) )
      {
         snprintf( buf2, MAX_STRING_LENGTH, "&R[&z%-15.15s&R]&w  ", ability_name[iClass] );
         mudstrlcat( buf, buf2, MAX_STRING_LENGTH );
         if( ++col % 4 == 0 )
         {
            mudstrlcat( buf, "\r\n", MAX_STRING_LENGTH );
            send_to_desc_color( buf, d );
            buf[0] = '\0';
         }
      }
   }
   
   if( col % 4 != 0 )
      mudstrlcat( buf, "\r\n", MAX_STRING_LENGTH );
   mudstrlcat( buf, "&z:&w ", MAX_STRING_LENGTH );

   send_to_desc_color( buf, d );
   d->connected = CON_GET_NEW_CLASS;
}

Why this should be done.... If someone put in random race, or non existant... it never checked, therefor it would crash mud. Wtih this fix it will ensure this does not happen