Kripke's approach says that it triggers a "partial predicate" which is neither true nor false, which fails to explain its "strengthened" version, which does not require the concept of falsehood.  
It supposedly caused the death of Philetas of Cos.  Tarski's Undefinability Theorem holds that it does not constitute a legitimate declarative sentence, and thus it cannot exist in "classical formal language."  Other solutions include the rejection of secondary evaluations, under which its subject is simply false.  Kripke's approach says that it triggers a "partial predicate" which is neither true nor false, which fails to explain its "strengthened" version, which does not require the concept of falsehood.  FTP, name this paradox arising from the sentence, "This sentence is false."
It supposedly caused the death of Philetas of Cos.  Tarski's Undefinability Theorem holds that it does not constitute a legitimate declarative sentence, and thus it cannot exist in "classical formal language."  
liar paradox (accept early "This sentence is false" or equivalents)