From Dennis Guse: I had some issues with a latex document as it contained several UTF-8 unbreakable whitespaces (actually in the bibtex due to copy and paste of titles from PDF documents). However, latex does not (yet) understand this special whitespace and only returns an error with unknown UTF-8 character.

The following line adds the unbreakable UTF-8 whitespace, so latex understands it. \DeclareUnicodeCharacter{00A0}{~} %Unbreakable spaces

See also #126