I use FastPictureViewer Pro to rename my images after I've done the initial culling on a card or hard drive). And I've noticed with the current and previous versions of the program when it encounters some errors while doing the renaming, the error dialog, which should detail what the errors are, is always completely blank. Yet when I look at the images it appears they have all been correctly renamed which is why I kept forgetting to mention this before now.
In case it matters here is the renaming mask I use:
{DateTakenUtc:Year}_{DateTakenUtc:Month0}{DateTakenUtc:Day0}_{DateTakenUtc:Hour0}{DateTakenUtc:Minute0}{DateTakenUtc:Second0}_{DateTakenUtc:Millisecond0}
It doesn't seem to matter what kind of images I'm renaming either, JPGs or CR2s.