Netbeans will show errors in some of the vendor files because, well, they contain "errors". For example, under the Sensio generator bundle, there are some template type controller files with a php extension. The files themselves are not valid php and hence get flagged by netbeans.
It is annoying but it's just something you have to ignore. Or maybe coax the vendors to tweak their code. Some folks are trying to get netbeans to skip these sorts of errors but no luck so far.
More info here: https://netbeans.org/bugzilla/show_bug.cgi?id=226954