I multibox over a number of computers. When I setup GCP I told it where WoW was located. When I added additional characters (on a different computer) it expected to find WoW in the same folder on the same drive. If I changed one WoW location it would chance them all.
On my main computer, WoW exists in C:\Program Files\World of Warcraft. On my clone computers WoW exists in the root of F: and E: drives.
In order for GCP to work properly I had to use SUBST (DOS command for those who are not of the DOS generation).
From the "Select Profile" screen (when you first start GCP), select a team, click the "Edit" button, then unclick "Auto Fill", bottom right of the team configuration screen.