I had a possibly related problem. Download files are a custom post type called 'dlm_download' and they were showing up in search results, which I did not want. Even though I saw 'exclude_from_search' => true, on line 345 of download-monitor.php, the files still showed up in search results, then clicking on the result threw an error. But I then saw that the post_type being registered there was 'dlm_download_version,' not 'dlm_download'. When I added the same line to the function call to register_post_type() for dlm_download, search results for the download file went away. I needed to do this because the download link is embedded in a post that contains a description, an image, etc. Did not want the search results to return both that post, and the download file separately. Seems to be working ok now.