Another possible issue can occur after the app successfully downloads, but then won't install. The following is a fix for this issue.
I discovered this little nugget of information on another developer's blog - Angry Mob Games, another cool group of folks who use Unity to develop apps. Word is these steps can help you install apps onto your SD card on certain phones that are a little picky otherwise. The following is quoted from their FAQ, and most likely applies to any installation issues you may be having with Battleheart.
On certain devices/Android OS versions, there's a problem when installing the game to the SD card. This is true especially if you're seeing the 'Unknown Error 18' when installing the game, or updating it. To fix it, there are two options: the hard way, which fixes this for good, and the easy way, which you have to do each time you install an app.
- Connect your device to the computer via USB
- Mount the device as a USB drive
- Go to the '.android_secure' folder and delete the 'smdl2tmp1.asec' file
- Unmount the device and try to install the game again
- Uninstall Battleheart
- Unmount the SD card
- Clear the Marketplace cache and data in the Applications Manager
- Install Battleheart again
- Mount the SD card back
- Move the game to the SD card, if you wish