7-D won't fire with Flash

[unfocused]

Okay, this happened to me again tonight and I'm wondering if anyone is familiar with this phenomenon.

I was shooting some portraits using my 7D with two 580 EXIIs mounted off camera and a 430 EX II as a third light to separate the subject from the background. Triggering the flash through the on-camera infrared pop up.

Shooting RAW. Initially, while shooting, everything was going fine and then I began to have a problem where the shutter button would not work and the viewfinder readout says "busy."  I'd have to pause and wait for several seconds before it would clear and let me shoot. I'd get off one shot and it would do the same thing.

When this first happened, I thought the camera was waiting for the flashes to recycle, so I bought battery packs for the 580s. But, it still happens. I thought maybe it was the 430 not recycling, so tried shutting that down. Still hangs up.

This has happened on a number of occasions and I've tried several different things, but can't seem to figure out where the problem is. One time, I tried switching out the memory card, even though it wasn't full. That seemed to help, but not consistently.

Clearly, the camera is waiting for something to clear or recycle, but I can't figure out what it might be. Anyone else ever have this problem or have any ideas.

Thanks.

[Lawliet]

At first - that camera can't tell wheter there are remote flashes or not, it it doesn't wait for them to get ready.

That "busy" is caused by the popup flash, either it doesn't recharge fast enough or gets to hot.
Using a 580/Metz AF58 or pocket wizards helps. A somewhat slower shooting style is the much cheaper option.

[OnceUponaHoneyB]

If you are using the pop up flash as a  light source in addition to the master unit the pop up will take a long time to recycle. 
You can use the pop up only as the master and disable firing

[neuroanatomist]

Are you firing the popup flash to contribute to the exposure, in addition to a wireless master?  If so (and perhaps even if not), the holdup might be waiting for the popup flash to recycle (which takes substantially longer than a Speedlite).  If that's the case, an ST-E2 or an RF solution (e.g. PocketWizard) might be the answer (though not cheap, especially the PWs), or use a 580 as an on-camera master.

[unfocused]

Okay, I wondered about the pop up. I am not using it for the exposure, only to fire the strobes, but of course, to do so, it has to recycle and fire anyway.

It's strange because initially it all works fine. Recycles quickly without any problem. But, about halfway through a shoot it starts to hang up. I use a battery grip and the batteries are generally charged up, but maybe the pop up overheats or something after a few dozen shots.

I thought I might need to get an ST-E2, but wanted to get some confirmation before spending the money. 

Someone suggested a slower shooting style, so now I'm thinking I may try to pace myself a bit. Shoot a half dozen shots, wait a few minutes and shoot some more. Just a wild guess, but maybe if I can keep it from initially overheating it might work better than letting it overheat and then wait for it to cool down. What do others think?

[FiveRings]

Recycle should be in seconds, not minutes, unless you're chaining shots at full 8FPS burst.

Sounds more like you have an issue with your memory cards. What cards are you using?

[unfocused]

Cards are Lexar 300X or 400X. I doubt they are the problem. I checked around and found a reference on another forum to the pop up overheating. That does seem to be the most likely culprit.