Problem with .idx/.sub not opening

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I'm trying to open .idx + .sub subtitles for an avi file. But, when I go to the menu "Video / Subtitles", it says "Open file" rather than displaying the subtitle track options (e.g., 'Track 1'). If I click "Open file" and then choose the idx file, nothing happens. The subs don't appear, and the "Video / Subtitles" menu still shows "Open file" rather than showing any subtitle tracks.

The subtitles *do* display properly in Media Player Classic Home Cinema, so I know the idx & sub files are ok.

I'm using VLC 1.1.4 on Win 7 x64.
All 3 files (avi, idx, sub) have the exact same name except for the extension.
All are in the same directory.
I have reset my VLC preferences.
I have tried setting the "Subtitle autodetection fuzziness" at 1, 2, and 3.
I restart VLC each time a make a preference change.
I've tried using the "advanced open" dialogue and choosing both the avi and idx files.

The audio and video play perfectly.
The avi file is h.264, 848x478 resolution, AC3 audio.

Any suggestions on how to get the subtitles to work in VLC? Thanks in advance.