downloaded the nightly build, unzipped, started the .exe - errors during start-up before loading selected sources
Did they unzip on top of an existing installation? That shouldn't be done - it will cause this issue and many others.
ah - yes, I did just unzip on top of the existing folder. (I always have in the past and didn't expect a problem).
So I cleared the folder and repeated the unzip - runs clean!
I've noted this as something to beware of when I download nightlies in future...
fixed by doing a clean unzip