1 E=mc^2 is not the solution to E^2=(mc^2)^2. The solution is + or – E= + or – mc^2.
2 E=mc^2 is said to show how mass (kg) 'no longer exists as or with mass but 'converts into' massless energy (kgm^2/s^2) and visa versa.
1st Equals does not mean, anywhere else in maths, science or language; converts into. Everywhere else in maths, science and language equals means; both sides of the equation or statement are just two different ways of saying the exact same thing. Ordinary water ice = ordinary frozen water, frozen water does not disappear and convert into ice. Feline = cat. Any statement that equate equals with converts into, is nonsense.
2nd Energy is, wait for it, kgm^2/s^2. Mass times the speed of light squared, mass (kg) times c (m/s) squared. Energy has mass, as shown by an understanding of maths, units and what an equals sign actually means.
FTJSMbyEED (C) 2012 Angela Michelle Joy Stahlfest-Moller.
E^2 = matter with existence in time, volume, mass and charge spinning with respect to itself (mc^2)^2 + the same matter with existence in time, volume, mass and charge moving with respect to everything else (pc)^2. ©
Without matter, with existence in time, volume, mass and charge, moving per second along a distance there is no energy.
Without matter moving per second there is no force.
Without matter moving there is no momentum.
Without matter there is no thing, nothing.
Nothing except empty space existing in time.
Massless is not possible. FTJSMbyEED (C) 2012 Angela Michelle Joy Stahlfest-Moller.