Facelets is a XML based view technology. XML has only five predefined entities. The is not among them. It works only when used in plain HTML or in legacy JSP (note: it doesn't work in JSPX as that's also XML based!).
To fix this, you either need to declare the entity yourself in the doctype of the very XHTML file containing the entity,
<!DOCTYPE html [
<!ENTITY nbsp " ">
]>
or, better, use the (hexa)decimal notation instead:
  or  
In an average IDE it should be trivial to perform a "find and replace in all files" and replace every occurrence of by  .
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