OK - I posted about this in the Tethering thread, but I'll write about it again.
This has happened to me SEVERAL TIMES. Usually waiting a few hours, and rebooting several times, fixes it.
NEXT TO the X with the zero bars highlighted (your 'reception bars'), Do you have the picture of the Target? Or not? It's just to the left of your bars, typically...
(edit: If you DO have the picture of the target next to your empty bars, WAIT with your Eris on the lock screen. The bars will appear eventually! If you try to unlock the phone too quickly, you might run into trouble!)
If you don't have the picture of the target, your phone and the tower are NOT EVEN ADDRESSING one another. In other words, you're NOT on the Verizon network. Either you had VERY bad reception at boot (which hasn't been proven to do this), there is a flaw in the antennae of our phones, or you got kicked off the Verizon network temporary (like I contend that I did).
I used PDANet for hours several times, and when rebooting my phone RIGHT after using lots of bandwidth, I got this problem. The other night it happened so badly and for so many hours that I had to hard reset my phone. Even on the phone with Customer Service, the lady had to 'force through' my *228 (and get a manager to do it after 5 tries). If you're using tons of bandwidth, perhaps your account is getting flagged?
Otherwise, I only had this happen once. I kept using ES File Manager to uninstall random apps, and assumed it was those things causing the problem.
But with no network, ALL of the native apps force close. You have to be connected to a tower, or all of those apps that have to have 'a network' (not "mobile network" for data, just the standard talk-on-the-phone network) will force close.
Your Eris just went from an iPhone to an iPod.
Keep rebooting. If it doesn't work, Settings > Security > Factory data reset.
Make sure you save all your dirty MMS pictures from your girlfriend that are still in your Messages program, to your SD Card first. I'd find some WiFi and make sure my Google Contacts are synced (unless they already are, then you're all set).
I had to do this. Lost all my scenes. I was mad. But now I don't reboot my phone subsequent to tons of data. And I only reboot it during the day when I know I can go to a Verizon store and bitch!