Palm's App Catalog appears to have suffered a meltdown of sorts, with users of Palm Pre, Pixi, Pre Plus and Pixi Plus handsets reporting that after having downloaded a new title - whether paid or free - no aftermarket software will run properly. The issue remains even after fully erasing and restarting the phone; in fact, the apps are still installed even after that process is completed. However core functionality - calls, messaging and data - are all unaffected.
At the moment, a workaround appears to involve setting the date of the smartphone back to some point in April, but the official Palm blog is suggesting that an official fix will be appearing in short order. They also say that any purchases you've made through the webOS App Catalog have "been properly recorded and as soon as this issue is resolved, you’ll be able to access all apps you've purchased" so you shouldn't have to worry about losing money.