diff --git a/Ethernet/Socket_APIs_V3.0.2.chm b/Ethernet/Socket_APIs_V3.0.2.chm
deleted file mode 100644
index 5ed4b92..0000000
Binary files a/Ethernet/Socket_APIs_V3.0.2.chm and /dev/null differ
diff --git a/Ethernet/Socket_APIs_V3.0.3.chm b/Ethernet/Socket_APIs_V3.0.3.chm
new file mode 100644
index 0000000..35ed512
Binary files /dev/null and b/Ethernet/Socket_APIs_V3.0.3.chm differ
diff --git a/Ethernet/socket.c b/Ethernet/socket.c
index 4d16129..b289da4 100644
--- a/Ethernet/socket.c
+++ b/Ethernet/socket.c
@@ -199,7 +199,9 @@ int8_t close(uint8_t sn)
 	CHECK_SOCKNUM();
 //A20160426 : Applied the erratum 1 of W5300
 #if   (_WIZCHIP_ == 5300) 
-   if( ((getSn_MR(s)& 0x0F) == Sn_MR_TCP) && (getSn_TX_FSR(s) != getSn_TxMAX(s)) ) 
+   //M20160503 : Wrong socket parameter. s -> sn 
+   //if( ((getSn_MR(s)& 0x0F) == Sn_MR_TCP) && (getSn_TX_FSR(s) != getSn_TxMAX(s)) ) 
+   if( ((getSn_MR(sn)& 0x0F) == Sn_MR_TCP) && (getSn_TX_FSR(sn) != getSn_TxMAX(sn)) ) 
    { 
       uint8 destip[4] = {0, 0, 0, 1};
       // TODO
@@ -209,8 +211,15 @@ int8_t close(uint8_t sn)
       // ex> wait_1s();
       //     if (getSn_TX_FSR(s) == getSn_TxMAX(s)) continue;
       // 
-      socket(s,Sn_MR_UDP,0x3000,0);
-      sendto(s,destip,1,destip,0x3000); // send the dummy data to an unknown destination(0.0.0.1).
+      //M20160503 : The socket() of close() calls close() itself again. It occures a infinite loop - close()->socket()->close()->socket()-> ~
+      //socket(s,Sn_MR_UDP,0x3000,0);
+      //sendto(s,destip,1,destip,0x3000); // send the dummy data to an unknown destination(0.0.0.1).
+      setSn_MR(sn,Sn_MR_UDP);
+      setSn_PORTR(sn, 0x3000);
+      setSn_CR(sn,Sn_CR_OPEN);
+      while(getSn_CR(sn) != 0);
+      while(getSn_SR(sn) != SOCK_UDP);
+      sendto(sn,destip,1,destip,0x3000); // send the dummy data to an unknown destination(0.0.0.1).
    };   
 #endif 
 	setSn_CR(sn,Sn_CR_CLOSE);
diff --git a/README.md b/README.md
index 5c09e42..e6d130f 100644
--- a/README.md
+++ b/README.md
@@ -27,6 +27,9 @@ This driver provides the Berkeley Socket type APIs.
     - Define what Host I/F mode is used in **wizchip_conf.h**
 
 ## Revision History
+  * ioLibrary V3.0.3 Released : 03, May, 2016
+    * In W5300, Fixed some compile errors in close(). Refer to M20160503
+    * In close(), replace socket() with some command sequences. 
   * ioLibrary V3.0.2 Released : 26, April, 2016
     * Applied the erratum #1 in close() of socket.c (Refer to A20160426)
   * ioLibrary V3.0.1 Released : 15, July, 2015