Without seeing the book, this is always hard. It sounds like there was a conversion problem with going from PRC to epub. And that when that version was put on your Touch and then removed, it hasn't been cleaned up properly.
A few things I would try are:
- Open the ePub book with Sigil or use ePubCheck (not sure if that's the right name) to see if there are any errors. If you makes changes in Sigil an save them, make sure you delete the epub from the Touch before sending it over again.
- Change the title or author in the calibre metadata and then use "Save to disk" to get the ePub to the device. It doesn't matter if you save directly to the device or to the PC and copy it over manually. The idea is to make sure the file name of the ePub is different so that the device sees it as a different book. The change to the title or author will make sure you can find it on the device.
- Log out of the device and then back in. This will put a new database on the device. Unfortunately, you will lose the reading status of any sideloaded books and will need to redownload the kepubs.
- Do a factory reset. This should be overkill, but, it is also likely to solve the problem. After doing this you will need to put your sideloaded books on again and download the kepubs.
If you want, you can send me the database from the device and the book or put them somewhere to download. Then I can have a look through them and hopefully see what the issue is. Send me a PM for my address, or the download location if you do it that way.