Hello,
I ran into the same problem trying to use the Particle: Flash application (local) option. When I checked
C:\Users\<YourUsername>\.particle\toolchains\buildtools\1.0.0\bin I found that the cp.exe file was missing. It appears that the cygwin1.dll is the 64 bit version 2.10.0. I copied over cp.exe from my current 64 bit version of cygwin which is at 2.11.1 and it worked fine.
Hope this helps.
digitalhack