Think I got one
[2015.02.06-16.56.54:220][ 0]LogThreadingWindows:Error: Runnable thread FileConstructorThread crashed.
[2015.02.06-16.56.54:220][ 0]LogWindows: === Critical error: ===
Assertion failed: NewPosition >= 0 [File:D:\BuildFarm\buildmachine_++depot+UE4-LauncherReleases\Engine\Source\Runtime\Core\Private\Windows\WindowsPlatformFile.cpp] [Line: 59]
KERNELBASE.dll!UnknownFunction (0x00007ff92a4e606c) + 0 bytes [UnknownFile:0]
EpicGamesLauncher.exe!UnknownFunction (0x00007ff66107a86d) + 0 bytes [UnknownFile:0]
EpicGamesLauncher.exe!UnknownFunction (0x00007ff66102a318) + 0 bytes [UnknownFile:0]
EpicGamesLauncher.exe!UnknownFunction (0x00007ff661016518) + 0 bytes [UnknownFile:0]
EpicGamesLauncher.exe!UnknownFunction (0x00007ff661079e94) + 0 bytes [UnknownFile:0]
EpicGamesLauncher.exe!UnknownFunction (0x00007ff660fe9c50) + 0 bytes [UnknownFile:0]
EpicGamesLauncher.exe!UnknownFunction (0x00007ff660fc9b37) + 0 bytes [UnknownFile:0]
EpicGamesLauncher.exe!UnknownFunction (0x00007ff661029622) + 0 bytes [UnknownFile:0]
EpicGamesLauncher.exe!UnknownFunction (0x00007ff6613f70a4) + 0 bytes [UnknownFile:0]
EpicGamesLauncher.exe!UnknownFunction (0x00007ff6613e748c) + 0 bytes [UnknownFile:0]
EpicGamesLauncher.exe!UnknownFunction (0x00007ff661400475) + 0 bytes [UnknownFile:0]
EpicGamesLauncher.exe!UnknownFunction (0x00007ff661079cf6) + 0 bytes [UnknownFile:0]
EpicGamesLauncher.exe!UnknownFunction (0x00007ff661071d1c) + 0 bytes [UnknownFile:0]
KERNEL32.DLL!UnknownFunction (0x00007ff92b0916ad) + 0 bytes [UnknownFile:0]
ntdll.dll!UnknownFunction (0x00007ff92d0f4409) + 0 bytes [UnknownFile:0]
ntdll.dll!UnknownFunction (0x00007ff92d0f4409) + 0 bytes [UnknownFile:0]
Crash in runnable thread FileConstructorThread