When creating your keys, Cryptee uses a hashing algorithm (SHA256) provided by OpenPGPjs to mask the information for your safety.
This algorithm / implementation happens to dislike what programmers call "wide-characters". A good example of a wide-character is the "€" symbol.
So to prevent further issues from happening with your key, Cryptee warns you if you happen to have a wide-character in your key.
We're sorry for the inconvenience this may cause.