The new regulations have created 'a devil of' a problem [=a very difficult problem] for many small businesses.
He had 'a devil of a time' getting another job. [=he found it very difficult to get another job]
The shoes look great, but they're 'the devil' to walk in. [=they are very difficult to walk in]
(..) What's the meaning of this? You've been into Farmer Maggot's crop! You get back here! Get out of my field! You'll know the devil if I catch up with you! I don't know why he's so upset. It's only a couple of carrots. And some cabbages. And those three bags of potatoes that we lifted last week. (..)2001 The Lord of the Rings: The Fellowship of the Ring