Originally Posted by kovidgoyal
URL encoding the path is normal. calibre uses a Qt library function to open files with their preferred viewing application. This function requires URLs rather than file paths.
Thanks for the reply, in that case the problem probably originates from Qt, as the path is correct (it points to an actual djvu file, which I can access otherwise).
At the end of the month I will upgrade my Ubuntu installation to 9.10, I will see at that point if the issue solves itself or persists.