"An error occurred while preparing the installation. Try running this application again." High Sierra

Hi! I'm installing via the network recovery thing with OpenCore. Currently having an issue where the installer will get to about 3mins left, and then throw the error in the title. Happened twice. I followed the fix here, to no effect. My HDD is formatted as macOS Extended (Journaled).

I tried to erase the disk right after this happened the second time, but it said the disk is in use and I can't unmount it.

Other specs; - AMD FX-6300 - GTX 1050 - MSI 970 Gaming Motherboard

Any fix? Thanks in advance!