Not sure where I should post this, but...
I've been getting this error when trying to opt-in in the beta 117, since it was the version I was using before.
If I click "ok", Construct 2 opens, but it's still version 114.
I tried re-installing everything, checking the integrity cache, etc, but nothing works. If I opt-out of the beta, I still get the error, unless I reinstall it completely.
Another weird thing is that when I download it, it says the size is 300+ MB, but it actually is just 98MB.
It works normally if I don't opt in the beta, though.