Can you either make a public version of the project or a simplified public version that shows the problem? Or maybe upload a couple of screenshots onto imgur.com or photobucket to show the problem? One thought: in a schematic, netlabels (and volprobes in simulation schematics) with a space in them can cause some problems which are not always obvious. It might be worth checking that all the pin names and netlabels in your schematic and/or PCB are valid. Andy

Hey Andy, as I created a simplified example, the problem disappeared from the new version. It was not a question of spaces in names, that's for sure. It might have been something to do with the fact that this was an Eagle import, and running a DRC turned up a number of net errors, so I am not confident that schematic was any good (I'll return to it to further debug later). Meantime, I'll recreate it from scratch in EasyEDA to see what I get. Thanks!