OMG. Whitespace characters. There was a \r in the end of the filenames. You couldnt really see it when debugging 
because it looked fine in the log. I was also cutting the line from the log and using that to load, and it was fine.
The problem was, that some assets use a config file to load their mesh data. And some of those files had different line endings than that others. Uggh. Sorry to bother everyone. Stupid Dave again.