error trying to open source media file (ProRes 422 LT)

I have dozens of ProRes 422 LT files that were created by Red Cine-X (i.e., transcoded from R3D media). Compressor will read and further transcode them without complaint (albeit so slowly that I'm thinking I'd be better off using Red Cine-X again). However, with one file, which plays perfectly in Quicktime, and which Premiere Pro has no problems at all reading, Compressor complains (rather opaquely): "Error trying to open source media file."

There are some error messages in the Console window, such as:

3/12/16 3:13:53.219 PM mdworker[5752]: [15:13:53.219] FigFormatReaderCreateForStreamReturningMatchingContainerLabelType signalled err=-12848 (instantiationError) (Error creating FormatReader) at /Library/Caches/com.apple.xbs/Sources/CoreMedia/CoreMedia-1731.15.33/Prototypes /FormatHandlers/FigFormatReader_Common.c line 2157

Which might be relevant. But since compressor is so non-communicative about what its real error is, I don't know.

Anybody here know?