I'm having trouble using a remote reference in an Org-mode spreadsheet.

The Info node entitled "References" says that the first argument to the "remote()" expression "... can also be the ID of an entry, even in a different file, ...". What does this mean? What is the syntax for defining and referring to an "ID"?

I tried making a file called "report.org" like this:

* report output

:PROPERTIES:
:CUSTOM_ID: foo
:END:

| abcde | 17 |
| xyzzy | 42 |

And then I tried to refer to it from an Org-mode spreadsheet in a different file, like this:

#+TBLFM: @2$1=remote(file:report.org#foo, @2$2)

But it said "invalid reference".