Nested Editor de Textos Estructurados
The problem is quite common when you copy text from other sources like PDF documents into your source document. What happens is that there is some UTF-8 invisible / whitespace that you cannot see and that LaTeX is unable to interpret.
You can fix your document using sed command line program to replace all those invisible characters with nothing:
sed -i 's/\xe2\x80\x8b//g' [your_document].tex
Or in case of Nested files:
sed -i 's/\xe2\x80\x8b//g' [your_document].t2t
Fix for Nested will be published with Nested 2.0 so documents with whitespace UTF8 characters get automaticly converted.