@10basetom - thanks for reporting that. I think that error will have been in there for quite a while (since 1.5.3 back in May) but you are the first to notice/report it. I will fix it shortly.
The issue isn't the "u" (that is just a Python thing), it is that it doesn't have a full path to the location of the cover. Something that the 1.5.3 release made some intentional changes around (to allow users to copy their plugin config files between machines) but obviously I missed a spot to change...