program aa;
type
  point=^node;
  node=record
         data:integer;
         link:point;
       end;
var
  head,last,next:point;
  x:integer;
procedure insert(x:integer; var head:point);   {插入节点过程}
  var
    q,last,next:point;
  begin
    new(q);
    new(last);
    q^.data:=x;
    if x<=head^.data then begin             {如果x比第一个节点值小，插在最前面}
                            q^.link:=head;
                            head:=q;
                          end
                     else begin             {找到合适的位置并插入}
                            next:=head;
                            while (x>=next^.data) and (next<>nil) do {找位置过程}
                              begin
                                last^.link:=next;
                                next:=next^.link;
                              end;
                            if x<=next^.data then            {插入}
                                               begin
                                                 last^.link:=q;
                                                 q^.link:=next;
                                               end
                                             else          {插入到链表尾部}
                                               begin
                                                 next^.link:=q;
                                                 q^.link:=nil;

                                               end

                          end;

  end;

begin                {main}
  read(x);           {建立第一个节点}
  new(head);
  head^.data:=x;
  head^.link:=nil;
  read(x);           {开始插入数值}
  while x>=0 do
    begin
      insert(x,head);
      read(x);
    end;

  writeln;            {输出链表内容}
  next:=head;
  while next<>nil do
    begin
      write(next^.data:5);
      next:=next^.link;
    end;
end.



此程序在执行过程中出216号错误，请高手帮忙调试一下，看看错在什么位置。
我调试的时候主程序没发现错误。
附件里是源程序，下载后可以直接运行的。