What type of device is your device? You posted in the Mac Programming section, not the iOS Programming section...
Anyways, I would guess that both of your apps have the same bundle identifier. That's the thing that normally looks something like com.company-name.name-of-my-app
Make sure your bundle identifiers are different or the OS, whichever OS it is, will think they're the same and overwrite one with the other when you try deploying both on the same device.