Easy way to test would be to take a WMA file (any WMA file--for that matter, MuvAudio can transcode MP3s, right?, so you could take any MP3 as well) go into a tag editor for the file, and add an ellipsis to the end of the album title (should also work if you put an ellipsis at the end of the artist field, but album for sure,) then tell MuvAudio to output the file using WM/Arist Name & WM/Album Title (depending on the location of the ellipsis, the order may be important.)
I believe that the error occurs because Windows does not allow for folders to end with a period (let alone three of them,) but MuvAudio doesn't know that and tries to send the file to (for example) "The Mavericks - 20th Century Masters - The Millennium Collection..." instead of "The Mavericks - 20th Century Masters - The Millennium Collection" As a somewhat simpler way to express Windows' refusal to end a folder with a period, try naming a folder as an acronym (with the periods.) Want to install the game F.E.A.R. to \Games\F.E.A.R.? Well, too bad, you can't. You can install it to \Games\F.E.A.R or \Games\FEAR but not \Games\F.E.A.R.
As near as I can tell, MuvAudio just needs to learn that when it creates the output folders using embedded tag info that even if, according to the tag, the output folder should contain an ellipsis (or, for that matter, even a single period) at the end, that it needs to cut the ellipsis or period our of the picture. I've probably overexplained the situation, but on the off chance that I haven't and you want more clarification, just ask. I don't know squat about programming, but I have a pretty good handle on exactly why this error occurs. I think.