Linear A is an undeciphered script used in ancient Crete. Its decipherment is one of the "holy grailss" of ancient scripts.
A related script, Linear B, was deciphered in the 1950s by Michael Ventris as representing an ancient form of Greek.
Though the two scripts share many of the same symbols, using the syllables associated with Linear B in Linear A writings produces words that are unrelated to any known language. This language has been dubbed Minoan, and corresponds to a period in Cretan history prior to a series of invasions by Mycenean Greeks around 1400 BC.
As the Minoan language is lost to the modern day, it is unknown whether or not this is the correct decipherment, or merely gibberish being generated by an incorrect mapping of symbols to sounds. Until further breakthroughs are made, the content of documents written in Linear A remains a mystery.