Exception thrown when attaching debugger to unity process

Unity Engine
1

(apparently from the mono.dll thread)

Exception thrown at 0x0000000022B995DC in Unity.exe: 0xC0000005: Access violation reading location 0x0000000000000000

I am not playing my project. The exception is triggered both when I:

a) Attach the debugger and then load my project
b) Load my project and then attach the debugger

I am working in Windows unity 5.4.0f3 (64-bit) and my project includes a native plugin that I am developing.

What could be triggering an exception at debugger attach time before the project and my plugin even get a chance to run?

2

I updated my Unity version and problem seems to have gone away.