Something is amiss. You should be getting 240v pole to pole (hot to hot, whatever you want to call it) and 120v from each leg to ground. Where are you taking these measurements and with what?

I'd assume that you have 240v coming into the house, otherwise you would have probably noticed and mentioned that half the lights in your house are out. Unless you're missing a leg and something is backfeeding somewhere. A 240v appliance (water heater, a/c, etc.) can do that but they won't run right. So flip the main breaker probe your main feed and make sure you have 240v. If not, call the power company and/or a qualified electrician. Then disconnect the wires from the new 50 amp breaker, turn if off and back on (it's not entirely uncommon for one of the two poles to trip without appearing to have tripped). Do you have 240v there? If so there's something wrong with your wiring.

If you are using a "skinny" two pole breaker (GE), make sure it is installed correctly so that it contacts each bus bar, not just one.

Yep, the first place I'd go look is the output terminals on the breaker in the main panel. If it displays the same odd behavior, something is wrong there, somehow poles of the breaker are on the same leg.

Does it behave any differnetly with one or the other breaker turned off? How are you taking this reading. It's quite possible that you are reading stray coupled voltage (essentially an unterminated wire). It gets a nice potential to ground, but a measurment between the two floating wires reads nothing.

Problem solved. I was on the last two positions of the main breaker box and they happened to be on the same 110 lug. I move the double pole breaker up one position and moved the bottom 110 breaker down and that gave me 240 across the double pole 240 breaker. Thanks for everyones help.