Given that everything's on manual, that you're firing the flash at full power (1/1), and that you think waiting one second between shots is sufficient, I'm going to take an educated guess and say that your problem is that you're not waiting for the flash to fully recycle before you take a shot and/or you've got the power level on the flash set too high. It could also be that your batteries are not in good health or are not fully charged.

Adjust your expectations on how long it takes a flash to cycle: the recycle time for a full-power burst in the 430EX's specs is 3.7 seconds with alkalines, 2 seconds with NiMh rechargeables. Your flash is run on little AA batteries. These don't prove a huge amount of juice. Your flash uses a capacitor to store charge that it draws from the batteries over time, and then when you fire the flash, all that charge is released at once. But drawing a full-power burst's amount of charge takes time. This is why I asked if you're waiting until the PILOT button lights up red before you take the shot. While it's recharging the capacitor, the flash's PILOT button will be green. It will light up red when the capacitor is full and the flash is ready to fire again.

You can reduce the power requirements for a recycle by reducing the power setting on the flash. If you were down at 1/16 power, chances are good you could easily pop off shots at 1 second intervals without too much of an issue--although you might run the risk of overheating the flash if you do it too many times in a row too quickly. Never use burst mode when shooting flash in a studio unless you know you can use a very low level of flash.