I am running Guide 8 on Wine and I have just successfully created an the overlay using the procedure Christian describes. I am using Crossover 14.0.1 which is based on Wine 1.7.25.
Date: Sun, 30 Nov 2014 12:04:37 -0800
Subject: Re: [guide-user] Missing file when edifying new overlay
just a guess, because I had installed Guide 8 on a MACbook with Virtualbox some time ago.
When transferring Guide files to the MAC (via an iso file), they became write protected.
(Please don't beat me, if this is not the case; ... just wanted to help).