Lt General Flynn is guilty of requesting immunity to tell the truth

Makes no sense for Lt General Mike Flynn to seek immunity to testify and tell the truth to the Senate Intelligence Committee when he swore to be loyal to the United States, as an officer. 

Although Lt. Gen Flynnis is a retired army officer, it's certainly duplicitious for him to collude with foreign nations, like Russia and Turkey, when he had a career of pledging allegience to America, as in this Officer's Pledge:

Oath of Commissioned Officers

I, _(Michael Flynn)____, having been appointed an officer in the Army of the United States, as indicated above in the grade of _(Lt General)____ do solemnly swear (or affirm) that I will support and defend the Constitution of the United States against all enemies, foreign and domestic, that I will bear true faith and allegiance to the same; that I take this obligation freely, without any mental reservations or purpose of evasion; and that I will well and faithfully discharge the duties of the office upon which I am about to enter; So help me God." 

Lt. General Flyn was identified as a source for poential Russian blackmail. So, as a result of this potential intelligence coopting by Russia, Donald Trump was forced to fire him, as chair of the National Security Council.  

There is no reason for a senior US Army officer to need immunity from prosecution to testify under oath, if he is, in fact, innocent of duplicitous communication with Russia. Otherwise, by seeking immunity, Lt General Flynn is acting like he's guilty of treason and, quite frankly, his request for immunity is a desperate plea for help.