+1 for the above posts:
Besides checking/replacing the batteries, make sure that there is a solid connection with the hotshoes on the flash/receiver and the camera/transmitter. Use the test button on the transmitter to check for consistency (you don't even need to have the flash plugged and/or turned on - just watch the light on the receiver).
Someone mentioned different types of batteries - NiMH batteries typically run at 1.2v (alkalines are 1.5v), and some devices will not run at this reduced voltage (I can't use my Maha Powerex batteries in my Nintendo Wii remotes because of this). I have not tested to see if they work in the YN-460 flashes.
Also, what flash power setting are you at? I thought I had a problem with both of my YN460's, but I actually wasn't letting them charge all the way before snapping the picture (I was used to the relatively quick recycle times on my Canon 430EX).
As far as radio interference goes, make sure you keep your cell phone away from the transmitter or receiver (don't keep it in your shirt pocket - 8-12" away from the camera). I know they run on different frequencies (1.8ghz for my phone and 2.4ghz for the RF-602's), but I always had a problem with my phone messing stuff up. In addition to screwing up my flash transmitter, if I leave my phone sitting next to my mouse, I get strange intermittent glitches. Some info here: http://en.wikipedia.org …c_interference_at_2.4_GHz