Most likely your iPhone or iPod Touch has a firmware previous to the 2.2.-release.
The best solution is to download the most recent free upgrade provided by Apple on iTunes, and then try to download iCaramba Spanish Course again.
We do, however, have a version of iCaramba Spanish Course for previous releases of the firmware (2.0 and 2.1).
This has not been released due to low demand, but if you send us a message in the
contact-form requesting it, we will make it available to you.