After testing, I have found that the game crashes if one is playing on Windows 10 Technical Preview. I've tried a custom game with 
and with 
and the same crash occurs, however in custom games, the SR map becomes dyed in a sepia tone.
schIep4 votesI'm having the same problem, however I'm on a Mac. I don't know if it's the patch or my Mac. I don't really think it's my Mac though, because I was playing during the 5.4 it was working perfectly.
Squeester2 votesI'm having the same problem, however I'm on a Mac. I don't know if it's the patch or my Mac. I don't really think it's my Mac though, because I was playing during the 5.4 it was working perfectly.
This has been happening for me on mac since 5.4. Haven't really been able to play league for a week... which really sucks when you've put over a hundred dollars into an account xD Super pissed this wasn't fixed in 5.5.
sigh
Lyn Lee Poo2 votesI can confirm this is happening with me as well.
Windows 10 Technical Preview, after patching to 5.5 the game crashes 3 seconds after joining the game. Can't reconnect to my game, and now i'll likely be labeled a leaver. 
MemeFraiche2 votesI cant even start the game without it crashing my entire computer. I'm on Windows 8.
Lumber Foot1 votesSame issue here! Both my friend and I use windows 10 tech preview, and 5.5 broke the client. You connect, after 3 seconds it crashes everytime. Please fix this riot! We can't play the game.
che1o1 votesALL win10 users experience the same problems after the loading screen..mostly because of compatibility reasons..even in pbe before patch 5.5 was launched on all servers the game already had this issue.. Anyway, I reconnected to the game restarting and choosing windows 8.1..so those of you who have only win10, you should try to reconsider the risks of a "TECHNICAL PREVIEW" on some programs..
TeemoJenkins1 votesCan you guys help me understand something? As beta testers, why do you expect live software to be updated for a beta operating system? Riot could spend thousands of development dollars trying to make it work in Windows 10 only for Microsoft to patch it and make it not work again? Live Applications are built for released operating systems, not beta. When you agreed to be a beta tester for Microsoft in the agreement it says it's not recommended to install and expect viability of end user applications. Sorry it's broken for you, but as a beta tester that's literally what you signed up for - to find issues and report them. My 10 received an update yesterday, don't know about yours and now most of my DirectX applications aren't working - I would image that's the root cause, and as a beta tester I reported to Microsoft, not Riot.
Kreed3 votesYou report it to both. And that's why you test, to provide feedback for companies. What I can't understand is how so many people have an issue understanding that is what they signed up for.
Norozza1 votesThat's funny cause all my games work just fine (other than league) after the update so I'm pretty sure you are having a directx issue not a windows 10 issue.
Bladetrain3r3 votesThis is why we are reporting the issue, the game crashes on Windows 10 now and if nobody reports it what happens when MS releases the OS? I'm sure people have also reported it on Windows feedback. Just because Riot isn't obligated to investigate that doesn't mean they wouldn't like to know about potential problems?
We're not saying Riot needs to put maximum priority on fixing this (though it would be nice since I've just been labelled a leaver in a ranked game) but if they're aware of the issue maybe they can put a little time into investigating to make things easier for people now and in the future.
I get the same issue, Win 10 64, build 9926.
For reference, event log does log an application fault:
Log Name: Application Source: Application Error Date: 3/12/2015 10:34:21 PM Event ID: 1000 Task Category: (100) Level: Error Keywords: Classic User: N/A Computer: WIN-RKN2P1Q69N9 Description: Faulting application name: League of Legends.exe, version: 5.5.0.266, time stamp: 0x54fa639c Faulting module name: unknown, version: 0.0.0.0, time stamp: 0x00000000 Exception code: 0xc0000005 Fault offset: 0x00000000 Faulting process id: 0xa7ac Faulting application start time: 0x01d05d03e033f95d Faulting application path: C:\League of Legends\RADS\solutions\lol_game_client_sln\releases\0.0.1.80\deploy\League of Legends.exe Faulting module path: unknown Report Id: 29a931d5-c8f7-11e4-9633-74d02b352967 Faulting package full name: Faulting package-relative application ID:
varucu2 votesYou may not believe this but Windows 10 developer preview is way better them the latest Windows 8 (official release).
Lee Zed Sin1 votesExact same issue here. Also in Win 10 preview.
Simplicate1 votesHaving a similar problem. I patched and didn't restart my PC so I thought that was the problem because when I ALT+esc out of the program then go back in the game would glitch in and out of windowed mode and I couldn't use any abilities, only pings. So I restarted and I tested ALT+esc again and the same bug appeared. Also getting a higher ping and lower frames than usual :/ So much for not ruining toasters huh Riot?
mennolord71 votesif i login my screen frozen i cant move my mouse and nothing help pls fix
kluggenhaim1 votesI'm having the same issue after 5.5 it crashes.. and very laggy in game.. Riot please do something!!
