AutoCAD external reference image can't be previewed in EPDM

I attached a external reference(image) in dwg file and check it in EPDM. In contains tab, the referenced file is listed. But only referenced directory is showed in Preview tab, not real image. One way is I can detach external reference, and embed a image block, then preview is fine.

But I wonder how to have external image referenced in Autocad drawing can be previewed in EPDM. Thanks!

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