[Solved] - JoinSession Blueprint error.

Unreal 4.7.0 Preview 6

I have made a very minimal game from the FirstPersonExample

The game presents a map with a menu of Host and Join as buttons.

Host works fine. You click host, it makes the session, and travles to /Game/FirstPersonBP/Maps/FirstPersonExampleMap.

On the client machine you click join and it finds the session ok, and tries to join it.
The log says…

[2015.02.12-05.19.52:980][343]LogBlueprintUserMessages: Join clicked
[2015.02.12-05.19.53:175][356]LogScript:Warning: Found a session. Ping is -1
[2015.02.12-05.19.53:361][367]LogBlueprintUserMessages: joined ok
[2015.02.12-05.19.53:367][367]LogNet: Browse: steam.76561197968250290//Game/FirstPersonBP/Maps/Entry
[2015.02.12-05.19.53:367][367]LogInit: SteamSockets: Socket queue 32768 / 32768
[2015.02.12-05.19.53:367][367]LogNet: error initializing the network stack
[2015.02.12-05.19.53:367][367]LogNet: DestroyNamedNetDriver IpNetDriver_0 [PendingNetDriver]
[2015.02.12-05.19.53:367][367]LogExit: PendingNetDriver IpNetDriver_0 shut down
[2015.02.12-05.19.53:367][367]LogNet:Warning: Travel Failure: [PendingNetGameCreateFailure]: SteamSockets: binding to port 0 failed (0)
[2015.02.12-05.19.53:367][367]LogNet: TravelFailure: PendingNetGameCreateFailure, Reason for Failure: 'SteamSockets: binding to port 0 failed (0)'
[2015.02.12-05.19.53:367][367]LogNet:Warning: Travel Failure: [ClientTravelFailure]: 
[2015.02.12-05.19.53:367][367]LogNet: TravelFailure: ClientTravelFailure, Reason for Failure: ''
[2015.02.12-05.19.53:383][368]LogNet: Browse: /Game/FirstPersonBP/Maps/Entry?closed
[2015.02.12-05.19.53:383][368]LogNet: Failed; returning to Entry
[2015.02.12-05.19.53:383][368]LogLoad: LoadMap: /Game/FirstPersonBP/Maps/Entry?closed

Any ideas why this would be?
The example is small so I could zip it up and send it if needed.

The menu blueprint script is…

I turned on very verbos for Online.
This is the client side log…

[2015.02.12-21.18.51:498][181]LogBlueprintUserMessages: Join clicked
[2015.02.12-21.18.51:606][182]LogOnline:Verbose: STEAM: Starting search for Internet games...
[2015.02.12-21.18.51:826][184]LogOnline:Verbose: STEAM: FOnlineAsyncEventSteamLobbyUpdate LobbyId: Lobby [0x186000036E35F0F]
[2015.02.12-21.18.51:936][185]LogOnline: Async task 'FOnlineAsyncTaskSteamFindLobbies bWasSuccessful: 1 NumResults: 1' completed in 0.340942 seconds with 1
[2015.02.12-21.18.51:936][185]LogOnline: STEAM: Found 1 lobbies, finalizing the search
[2015.02.12-21.18.51:936][185]LogOnline: STEAM: Search result 0: LobbyId=Lobby [0x186000036E35F0F], LobbyId.IsValid()=true, CSteamID(LobbyId).IsLobby()=true
[2015.02.12-21.18.51:936][185]LogOnline:VeryVerbose: OSS: GetBuildUniqueId: GEngineNetVersion 2440994 bUseBuildIdOverride 0 BuildIdOverride 0 Crc 427864428
[2015.02.12-21.18.51:937][185]LogScript:Warning: Found a session. Ping is -1
[2015.02.12-21.18.52:265][188]LogOnline:Verbose: STEAM: FOnlineAsyncEventSteamLobbyEnter LobbyId: Lobby [0x186000036E35F0F] Result: '1' k_EChatRoomEnterResponseSuccess (Success)
[2015.02.12-21.18.52:265][188]LogOnline:Verbose: STEAM: FOnlineAsyncEventSteamLobbyUpdate LobbyId: Lobby [0x186000036E35F0F]
[2015.02.12-21.18.52:265][188]LogOnline: Async task 'FOnlineAsyncTaskSteamJoinLobby bWasSuccessful: 1 Session: Game LobbyId: Lobby [0x186000036E35F0F] Result: '1' k_EChatRoomEnterResponseSuccess (Success)' completed in 0.221228 seconds with 1
[2015.02.12-21.18.52:265][188]LogOnline:VeryVerbose: OSS: GetBuildUniqueId: GEngineNetVersion 2440994 bUseBuildIdOverride 0 BuildIdOverride 0 Crc 427864428
[2015.02.12-21.18.52:267][188]LogOnline: Join session: traveling to steam.76561198036362562:7777
[2015.02.12-21.18.52:267][188]LogBlueprintUserMessages: joined ok
[2015.02.12-21.18.52:267][188]LogNet: Browse: steam.76561198036362562//Game/FirstPersonBP/Maps/Entry
[2015.02.12-21.18.52:267][188]LogInit: SteamSockets: Socket queue 32768 / 32768
[2015.02.12-21.18.52:267][188]LogNet: error initializing the network stack
[2015.02.12-21.18.52:267][188]LogNet: DestroyNamedNetDriver IpNetDriver_0 [PendingNetDriver]
[2015.02.12-21.18.52:267][188]LogExit: PendingNetDriver IpNetDriver_0 shut down
[2015.02.12-21.18.52:268][188]LogNet:Warning: Travel Failure: [PendingNetGameCreateFailure]: SteamSockets: binding to port 0 failed (0)
[2015.02.12-21.18.52:268][188]LogNet: TravelFailure: PendingNetGameCreateFailure, Reason for Failure: 'SteamSockets: binding to port 0 failed (0)'
[2015.02.12-21.18.52:268][188]LogNet:Warning: Travel Failure: [ClientTravelFailure]: 
[2015.02.12-21.18.52:268][188]LogNet: TravelFailure: ClientTravelFailure, Reason for Failure: ''
[2015.02.12-21.18.52:374][189]LogOnline:Verbose: STEAM: FOnlineAsyncEventSteamLobbyUpdate LobbyId: Lobby [0x186000036E35F0F]
[2015.02.12-21.18.52:375][189]LogOnline:VeryVerbose: OSS: GetBuildUniqueId: GEngineNetVersion 2440994 bUseBuildIdOverride 0 BuildIdOverride 0 Crc 427864428
[2015.02.12-21.18.52:375][189]LogNet: Browse: /Game/FirstPersonBP/Maps/Entry?closed
[2015.02.12-21.18.52:375][189]LogNet: Failed; returning to Entry
[2015.02.12-21.18.52:375][189]LogLoad: LoadMap: /Game/FirstPersonBP/Maps/Entry?closed

And the server side log…

[2015.02.12-21.18.33:079][970]LogWorld: Game class is 'FirstPersonGameMode_C'
[2015.02.12-21.18.33:082][970]LogAIModule: Creating AISystem for world FirstPersonExampleMap
[2015.02.12-21.18.33:084][970]LogWorld: Bringing World /Game/FirstPersonBP/Maps/FirstPersonExampleMap.FirstPersonExampleMap up for play (max tick rate 0) at 2015.02.12-14.18.33
[2015.02.12-21.18.33:085][970]LogWorld: Bringing up level for play took: 0.002202
[2015.02.12-21.18.44:646][687]LogOnline:Verbose: STEAM: FOnlineAsyncEventSteamLobbyChatUpdate User: [Sandswept] Bot [0x110000108D24C9C] Instigator: [Sandswept] Bot [0x110000108D24C9C] Result: '1' k_EChatMemberStateChangeEntered (Join chat)
[2015.02.12-21.18.44:646][687]LogOnline: STEAM: Updating lobby joinability to true.
[2015.02.12-21.18.52:985][204]LogOnline:Verbose: STEAM: FOnlineAsyncEventSteamLobbyChatUpdate User: [Sandswept] Bot [0x110000108D24C9C] Instigator: [Sandswept] Bot [0x110000108D24C9C] Result: '2' k_EChatMemberStateChangeLeft (Left chat)
[2015.02.12-21.18.52:985][204]LogOnline: STEAM: Updating lobby joinability to true.

Ok, we were missing in our DefaultEngine.ini the line

[/Script/Engine.GameEngine]
+NetDriverDefinitions=(DefName="GameNetDriver",DriverClassName="OnlineSubsystemSteam.SteamNetDriver",DriverClassNameFallback="OnlineSubsystemUtils.IpNetDriver")

Debugging further…

It says solved, but it doesn’t seem like it, were you only missing that line in the engine.ini?