Please read the title. 
then a code file changed and you tried to build while it was still updating the assemblies? is that possible
this happened to me with my asset on the store, it had a file since version 1.0 which had no problems in compiling or running, even with 3.4 it worked for some time, but one day i did a full reimport all of my project and there was a compiler error… i could not make it work so i just rewrote that part of the code in a different way, but this was way too weird and i dont know why it happened
Nothing in the Editor Log as well?