The IAA mentions that a LAN A340 declared mayday (and ATC confused it with one of the Ryanairs). It does not give any more details about that emergency as it's outside of its remit.
However, the aviation herald reported that it was in a much more critical situation than any of the Ryanair flights, having consumed 750 of the reserves.
The LAN also "lost" an engine. It would be good ti know if it might have been related to the critical low fuel situation.
BTW, it's good to note that the AVherald proved to have the facts right in its original report of the events of 26th July, and if anything went into more detail than the IAA report:
News: Thunderstorms in Madrid on Jul 26th 2012, landings, diversions, fuel emergencies and Ryanair