The judge in the trial of Tulisa Contostavlos told the jury there were "strong grounds" to believe an undercover reporter had "lied" at a hearing before the trial began.
Judge Alistair McCreath was speaking as he threw out the case at Southwark Crown Court.
The Sun's Mazher Mahmood - known as the 'Fake Sheikh' - had posed as a wealthy film producer when he met Contostavlos at a number of hotels and restaurants.
The former N-Dubz singer strongly denied that she had helped broker a drug deal between Mahmood and her rapper friend Michael Coombs, also known as Mike GLC.
More top news
A mother who revelled in the attention having a poorly child brought has been convicted of poisoning her son to death.
The Newcastle-based bakers made £1m a week in coffee sales in the period leading up to Christmas.
The Lib Dems have called on the UK to follow suit of countries like Portugal in treating drugs as a health rather than a criminal problem.