Well, I checked where the product name is verified in the stylevar data manager (where it displays that message if it fails), and it checks for the product name being 25 chars or less, and also only contains the chars A-Z,a-z,0-9 and _.
Now that I look at the code again, that may actually be a bug, because the comment says "check if longer than 25 chars..." but the code says strlen($product) < 25.