C# Remove Elapsed Event Handler From Timer Object

I'm doing some server side programming and trying to REUSE a System.Timers.Timer object without luck.

Here is what I want to be able to accomplish

 

System.Timers.Timer myTimer = new System.Timers.Timer(1000);
myTimer.AutoReset = false;
myTimer.Elapsed += delegate { OnMyTimer_Elapsed1(arg1,arg2);};//Yes I need to pass some args which are optional by the way
…
//then do some processing (this may take 500ms to 2000 ms)
…
If(something == true){
    //remove previous elapsed event handler from myTimer object
    myTimer.Elapsed -= delegate { OnMyTimer_Elapsed1();};//Notice -=

    //Then reattach different elapsed event handler
    myTimer.Elapsed += delegate { OnMyTimer_Elapsed2(arg1,arg2);}; 
}

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This code compiles fine but OnMyTimer_Elapsed1 event is firing TWICE when “something == true” where I was expecting that to be fired only ONCE in any case.

As you can see I'm trying to remove the event handler with "-=" without luck. Your assistance is much appreciated! thanks.