I would suspect a corrupt file. You may try to manually import some files and see if you can find the one(s) it is crashing on....
Yep.
The Logging should be able to help you track it down.
Startup logging (you can uncheck some of the clearly-unrelated loggers like Handheld, Store, and Podcast if you want to make the logfile easier for you to look through, but be careful and when-in-doubt at all leave it enabled). If you already had logging enabled, it will probably help to clear the log right before you start. Then, force it to do an Auto-Import Scan (Tools -> Import -> Run Auto Import Now). When it crashes, you can either:
1. Find the "Log.txt" file in your C:\Users\<username>\AppData\Roaming\J River\Media Center 16 folder
2. Reopen MC and go to
Help -> Logging -> View Previous LogStart looking down near the bottom, and check out the files it was working on,
and those "near" them, in the file system and you'll likely find your culprit(s). MC's Importer is multithreaded though, and it'll be working on more than one file at a time, so scan back from the "end" of the log a little ways and take note of a few of the different files mentioned. The log may clearly indicate which thread crashed, and then it should be easy to figure out. But it may also happen just as MC looks at the file for the first time, which means it won't be one of the files listed, but the "next" one in the queue after it finished one of the files listed (which is why I said to check out the ones "near" it).
When you find the files, often it will be fairly obvious. They might have zero file sizes, or unusually small/large file sizes for their "category". Or look for files that Windows doesn't "thumbnail" like the rest.
If you find your broken ones and you're not 100% on the source of them, it might not be a bad idea to check them for viruses before you delete them. Probably not, but you never know.