Command: ["sharedfolder", "add", "2850746f-ba92-4866-b3be-7871613e20b0", "--name", "somenamehere", "--hostpath", "\\\\?\\\\\\host.domain\\path_here"]
Stderr: VBoxManage.exe: error: Shared folder path '\\?\\\host.domain\path_here' is not absolute
VBoxManage.exe: error: Details: code E_INVALIDARG (0x80070057), component SharedFolder, interface ISharedFolder, callee IUnknown
VBoxManage.exe: error: Context: "CreateSharedFolder(Bstr(name).raw(), Bstr(hostpath).raw(), fWritable, fAutoMount)" at line 1015 of file VBoxManageMisc.cpp
Uninstalling Vagrant 1.8.1 and installing Vagrant 1.7.4 solved my problem for now -
shared folders mounted correctly.
config.vm.synced_folder "X:/some/path", "/some/path"
config.vm.synced_folder "X:/", "/some/path"