I am experiencing this problem too.
It happens when I hit the play button. Simple Blueprint Project, it started after adding a UMG widget.
MachineId:
EpicAccountId:
Access violation - code c0000005 (first/second chance not available)
UE4Editor!FEngineLoop::Tick() + 3657 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.5\engine\source\runtime\launch\private\launchengineloop.cpp:2154]
UE4Editor!GuardedMain() + 479 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.5\engine\source\runtime\launch\private\launch.cpp:133]
UE4Editor!GuardedMainWrapper() + 26 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.5\engine\source\runtime\launch\private\windows\launchwindows.cpp:125]
UE4Editor!WinMain() + 249 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.5\engine\source\runtime\launch\private\windows\launchwindows.cpp:201]
UE4Editor!__tmainCRTStartup() + 329 bytes [f:\dd\vctools\crt\crtw32\dllstuff\crtexe.c:618]