As reproduced on Windows Vista Home Premium (32-bit) SP2, with TrueCrypt 6.3a …
vssadmin list shadowstorage
vssadmin list shadows
vssadmin 1.1 - Volume Shadow Copy Service administrative command-line tool
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Error: The shadow copy provider had an unexpected error while trying to process the specified command.
Workaround: Unmount all TrueCrypt volumes.
Note that other vssadmin commands (List Providers, List Volumes, List Writers, Resize ShadowStorage) can be used while a TrueCrypt volume is mounted. Restore points can be created while a TrueCrypt volume is mounted.
I have found that if the truecrypt volume is mounted as a removable drive VSSADMIN LIST SHADOWS works.