I'm not sure what you mean by “export to LR”, you can't export to LR. In LR you would “import” files from a folder instead.
Regardless, if the file doesn't open properly in LR, either your camera is not supported by LR (updating LR to the latest would help in that respect) or your files have become corrupted somehow. Perhaps you can upload an example of a file that doesn't show in LR so we can have a look?