Action<object, EventArgs> could not be cast to EventHandler?

Action<Object, EventArgs> a = (o, ea) => { };
EventHandler e = a.Invoke;

Lambdas are implicitly convertible to delegate types with the right shape, but two same-shaped delegate types are not implicitly convertible to one another. Just make the local variable have type EventHandler instead.

EventHandler h = (o, ea) => { ... };
e += h;
...
e -= h;

(in case it helps:

Action<object, EventArgs> a = (o, ea) => { }; 
EventHandler e = a;  // not allowed
EventHandler e2 = (o,ea) => a(o,ea);  // ok

)

Declare your event as

public event Action<object, EventArgs> e;

Then you can directly add your action:

Action<object, EventArgs> a = something;
e += a;