diff --git a/incl_external_flag.php b/incl_external_flag.php
index bcd00dd..07237aa 100644
--- a/incl_external_flag.php
+++ b/incl_external_flag.php
@@ -58,6 +58,11 @@ $proj=$tid2proj_l[$tid];
 $pf=realpath(__DIR__."/".$proj["path"]."/handle_external_flag.php");
 
 if(!is_readable($pf)) {
+    $pf1=realpath(__DIR__."/".$proj["path"]."/automake_attachment.php");
+    if(is_readable($pf1)) {
+        gen_error_404("challange ".$proj["name"]." has been found, but the entry handle_external_flag.php does not exist. However, the entry automake_attachment.php was found. ARE YOU SURE this challenge is EXTERNAL?");
+        exit;
+    }
     gen_error_500("challange ".$proj["name"]." has been found, but the entry handle_external_flag.php does not exist.");
     exit;
 }
diff --git a/phplib/libcustomerrorgen.php b/phplib/libcustomerrorgen.php
index 07943bc..a8436d7 100644
--- a/phplib/libcustomerrorgen.php
+++ b/phplib/libcustomerrorgen.php
@@ -2,7 +2,7 @@
 
 function gen_error_400($reason="") {
     http_response_code(400);
-    echo "bad request: ";
+    echo "400 bad request: ";
     echo $reason;
     echo "\n";
     echo "٩(๑`^´๑)۶你对这个小程序做了什么哇...";
@@ -12,6 +12,7 @@ function gen_error_400($reason="") {
 
 function gen_error_404($reason="") {
     http_response_code(404);
+    echo "404 resource not found: ";
     echo $reason;
     echo "\n";
     echo "（⊙.⊙）这...这不对吧...";
@@ -21,6 +22,7 @@ function gen_error_404($reason="") {
 
 function gen_error_405($reason="") {
     http_response_code(405);
+    echo "405 method not allowed: ";
     echo $reason;
     echo "\n";
     echo "(／‵Д′)／~ ╧╧你到底在干什么啊";
@@ -30,7 +32,7 @@ function gen_error_405($reason="") {
 
 function gen_error_500($reason="") {
     http_response_code(500);
-    echo "internal error: ";
+    echo "500 internal error: ";
     echo $reason;
     echo "\n";
     echo "(✘Д✘๑ )哇啊！服务器居然出错惹...呜呜...｡ﾟヽ(ﾟ´Д`)ﾉﾟ｡";