This update is for an app downloaded with a different Apple ID. Sign in with that Apple ID and try again
What works for me is this hint from https://discussions.apple.com/thread/5532426?start=45&amp;tstart=0


  I solved this problem, instead of going to the update page go to the
  app itself within the App store.  Here it will say "Accept" where it
  usually says download and then it will reauthorize you