Download VDDK 5.1 and try to mount a remote vmdk on ESXi - it will fail.
If you have a look at the binary for vmware-mount.exe you will see that it is version
VMware DiskMount Utility version 4.2.0 build-751582
Copyright (c) 1998-2008 VMware, Inc.All rights reserved.
Probably/hopefully not the one that should be included.
Download 5.0 and remote mounts will work again