Whenever you need to specify the version for an item, you can use /version or /v. By default, it takes a changeset id, so don't use the C prefix with it. You can use L, D, or W if you want to specify a label, date, or workspace version respectively. There's another way to do that, by appending the version spec to the item path, for example: $/foo/bar;C123, in this case, you have to use the C prefix.