VMWare-Mount not recognizing virtual disks

I have two disks as .vmdk files, and four as .vdi files. I can boot virtual machines on them with Sun xMV VirtualBox, and they work just fine. However, I want to mount them on my local computer so I can read some files off of them without starting a virtual machine. I downloaded the vmware-mount utility, but I get this error, even when mounting .vmdk files, which should be VMWare images…

Unable to mount the virtual disk. The disk may be in use by a virtual
machine, may not have enough volumes or mounted under another drive
letter. If not, verify that the file is a valid virtual disk file.

Thinking it's a problem with the utility, I downloaded the SDK and made my own simple program in C to try to mount a disk. It just initializes the API, connects to it, then attempts to open the disk. I get this error, once again claiming it is not a virtual disk:

**LOG: DISKLIB-DSCPTR: descriptor above max size: I64u
**LOG: DISKLIB-LINK  : "f:\programming\VMs\windowstrash.vdi" : failed to open (The file specified is not a virtual disk).
**LOG: DISKLIB-CHAIN : "f:\programming\VMs\windowstrash.vdi" : failed to open (The file specified is not a virtual disk).
**LOG: DISKLIB-LIB   : Failed to open 'f:\programming\VMs\windowstrash.vdi' with flags 0x1e (The file specified is not a virtual disk).
** FAILURE ** : The file specified is not a virtual disk

The files are clearly virtual disks, though, since I can actually mount and use them with a virtual machine. I tried detaching them from any VMs and trying again, but I got the same results.

Any ideas? Maybe the "descriptor above max size" is a hint?

Some more info: the .vmdk disks were created on other computers. I just copied them to mine and created new VMs around them, but they work fine. All the .vdi files were created on my machine. Not sure if that affects anything.

Update: WinMount can mount the file.. so the problem seems to be with vmware-mount.