Index: binaries/data/mods/public/gui/common/network.js
===================================================================
--- binaries/data/mods/public/gui/common/network.js
+++ binaries/data/mods/public/gui/common/network.js
@@ -73,7 +73,6 @@
 	case 6: return translate("You have been banned");
 	case 7: return translate("Playername in use. If you were disconnected, retry in few seconds");
 	case 8: return translate("Server full");
-	case 9: return translate("Player identifier in use. If you were disconnected, retry in few seconds");
 	default:
 		warn("Unknown disconnect-reason ID received: " + id);
 		return sprintf(translate("\\[Invalid value %(id)s]"), { "id": id });
Index: source/network/NetClient.cpp
===================================================================
--- source/network/NetClient.cpp
+++ source/network/NetClient.cpp
@@ -31,7 +31,6 @@
 #include "ps/Compress.h"
 #include "ps/CStr.h"
 #include "ps/Game.h"
-#include "ps/GUID.h"
 #include "ps/Loader.h"
 #include "scriptinterface/ScriptInterface.h"
 #include "simulation2/Simulation2.h"
@@ -70,7 +69,7 @@
 CNetClient::CNetClient(CGame* game, bool isLocalClient) :
 	m_Session(NULL),
 	m_UserName(L"anonymous"),
-	m_GUID(ps_generate_guid()), m_HostID((u32)-1), m_ClientTurnManager(NULL), m_Game(game),
+	m_HostID((u32)-1), m_ClientTurnManager(NULL), m_Game(game),
 	m_GameAttributes(game->GetSimulation2()->GetScriptInterface().GetContext()),
 	m_IsLocalClient(isLocalClient),
 	m_LastConnectionCheck(0),
@@ -514,8 +513,10 @@
 
 	CNetClient* client = (CNetClient*)context;
 
+	CSrvHandshakeResponseMessage* message = (CSrvHandshakeResponseMessage*)event->GetParamRef();
+	client->m_GUID = message->m_GUID;
+
 	CAuthenticateMessage authenticate;
-	authenticate.m_GUID = client->m_GUID;
 	authenticate.m_Name = client->m_UserName;
 	authenticate.m_Password = L""; // TODO
 	authenticate.m_IsLocalClient = client->m_IsLocalClient;
Index: source/network/NetHost.h
===================================================================
--- source/network/NetHost.h
+++ source/network/NetHost.h
@@ -67,8 +67,7 @@
 	NDR_KICKED,
 	NDR_BANNED,
 	NDR_PLAYERNAME_IN_USE,
-	NDR_SERVER_FULL,
-	NDR_PLAYERGUID_IN_USE
+	NDR_SERVER_FULL
 };
 
 class CNetHost
Index: source/network/NetMessages.h
===================================================================
--- source/network/NetMessages.h
+++ source/network/NetMessages.h
@@ -113,11 +113,10 @@
 START_NMT_CLASS_(SrvHandshakeResponse, NMT_SERVER_HANDSHAKE_RESPONSE)
 	NMT_FIELD_INT(m_UseProtocolVersion, u32, 4)
 	NMT_FIELD_INT(m_Flags, u32, 4)
-	NMT_FIELD(CStrW, m_Message)
+	NMT_FIELD(CStr, m_GUID)
 END_NMT_CLASS()
 
 START_NMT_CLASS_(Authenticate, NMT_AUTHENTICATE)
-	NMT_FIELD(CStr, m_GUID)
 	NMT_FIELD(CStrW, m_Name)
 	NMT_FIELD(CStrW, m_Password)
 	NMT_FIELD_INT(m_IsLocalClient, u8, 1)
Index: source/network/NetServer.cpp
===================================================================
--- source/network/NetServer.cpp
+++ source/network/NetServer.cpp
@@ -29,6 +29,7 @@
 #include "network/StunClient.h"
 #include "ps/CLogger.h"
 #include "ps/ConfigDB.h"
+#include "ps/GUID.h"
 #include "ps/Profile.h"
 #include "scriptinterface/ScriptInterface.h"
 #include "scriptinterface/ScriptRuntime.h"
@@ -871,9 +872,27 @@
 		return false;
 	}
 
+	// Ensure unique GUID
+	CStr guid = ps_generate_guid();
+	int count = 0;
+	while(std::find_if(
+		server.m_Sessions.begin(), server.m_Sessions.end(),
+		[&guid] (const CNetServerSession* session)
+		{ return session->GetGUID() == guid; }) != server.m_Sessions.end())
+	{
+		if (++count > 100)
+		{
+			session->Disconnect(NDR_UNKNOWN);
+			return true;
+		}
+		guid = ps_generate_guid();
+	}
+
+	session->SetGUID(guid);
+
 	CSrvHandshakeResponseMessage handshakeResponse;
 	handshakeResponse.m_UseProtocolVersion = PS_PROTOCOL_VERSION;
-	handshakeResponse.m_Message = server.m_WelcomeMessage;
+	handshakeResponse.m_GUID = guid;
 	handshakeResponse.m_Flags = 0;
 	session->SendMessage(&handshakeResponse);
 
@@ -897,7 +916,6 @@
 
 	CAuthenticateMessage* message = (CAuthenticateMessage*)event->GetParamRef();
 	CStrW username = SanitisePlayerName(message->m_Name);
-	CStr guid = message->m_GUID;
 
 	// Either deduplicate or prohibit join if name is in use
 	bool duplicatePlayernames = false;
@@ -914,16 +932,6 @@
 		return true;
 	}
 
-	// Disconnect user if the provided GUID is already in use
-	if (std::find_if(
-		server.m_Sessions.begin(), server.m_Sessions.end(),
-		[&guid] (const CNetServerSession* session)
-		{ return session->GetGUID() == guid; }) != server.m_Sessions.end())
-	{
-		session->Disconnect(NDR_PLAYERGUID_IN_USE);
-		return true;
-	}
-
 	// Disconnect banned usernames
 	if (std::find(server.m_BannedPlayers.begin(), server.m_BannedPlayers.end(), username) != server.m_BannedPlayers.end())
 	{
@@ -1018,7 +1026,6 @@
 	u32 newHostID = server.m_NextHostID++;
 
 	session->SetUserName(username);
-	session->SetGUID(message->m_GUID);
 	session->SetHostID(newHostID);
 	session->SetLocalClient(message->m_IsLocalClient);