Ran into an issue to day installing Server 2012 R2 from an ISO file onto a fresh/brand new VM.

"0xE0000100: "Windows installation encountered an unexpected error. Verify that the installation sources are accessible, and restart the installation."

A little Google-Fu fixed me right up. New VM’s only have 512 MB of “startup memory” and you need to set it to at least 1024 MB to allow the installation to proceed without error.

I had Dynamic Memory setup with a range of 512 MB to 8192 MB and thought I would be okay. Not so. Anyhow, I just statically gave it 4 Gb for the install and changed it around once the install was finished. That being said, I am keeping the startup memory at 1024 MB now for all Server 2008R2+ VM’s.

Cheers!