I've run into the exact same issue.
I initially tried installing the 11.2 BETA 3 (first via the UI and then a fresh install via download), both wouldn't boot - it would hang just after the boot-loader splash on "booting....". Then installed 11.1 U6 and imported my previous config, Now in most places around the UI I receive the same error as @
achmetinternet all over the UI eg.
Is there any way I can use a previous config without using the UI, as the entire System menu doesn't load ?
Also all my jails and previously configured VM's seem to work.