Hi MatthewDay,
That Error 0x80070005 redirecting... message can be caused by a Windows Group Policy setting that disallows folder redirection (User Configuration\Administrative Templates\Desktop - Prohibit User from manually redirecting Profile Folders).
Can you check whether that policy setting is enabled? Either by checking your GPOs, or checking whether HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer contains a DisablePersonalDirChange value set to 1?