The Lebanese report blames pilot error for the crash of flight ET409, in which 90 people died, sources say.
But Ethiopian Airlines officials say the plane exploded, which they say points to sabotage, a lightning strike or shooting down.
The Lebanese report was due to be released on Tuesday.
The Addis Ababa-bound flight crashed minutes after take-off from Beirut in stormy weather on 25 January 2010, with no survivors.
Lebanese Transport Minister Ghazi Aridi told AFP news agency it was "clear" that "there were errors on the part of the pilot and co-pilot who are entirely responsible for the plane crash".
According to AFP, the Lebanese report says the pilot and co-pilot had been working non-stop for 51 days and were exhausted.
Mr Aridi said the plane was sound and transcripts of the exchanges between the crew and air traffic control on takeoff had not indicated any problem.
'Biased and incomplete'
Other officials say the report accuses the pilot of ignoring instructions from the control tower. Similar claims were made by Lebanese officials at the time of the crash.
But Ethiopian Airlines has vigorously denied the Lebanese findings in a statement, in which it insisted the crew was rested in accordance with regulation and the pilot had made appropriate efforts to control the aircraft.
"ATC [air traffic control] officers and other airlines' pilots have witnessed a ball of fire on the aircraft in the air," Desta Zeru, vice-president of flight operations for Ethiopian Airlines, said in the statement.
"The aircraft disintegrated in the air due to explosion, which could have been caused by a shoot-down, sabotage or lightning strike," he said.
The Lebanese report is "biased, lacking evidence, incomplete and did not present the full account of the accident", the statement quoted the airline's CEO Tewolde Gebremariam as saying.