Has an app ever started downloading from the Android Marketplace but then just disappears? I have had this problem for a few months now and have finally found a solution. This problem only occurred on some apps but if it did happen then the app would always refuse to download.
I have since found out that the problem is caused by the SD card. A folder on the SD card can become corrupt, once this happens apps that want to automatically install on your SD card will simply refuse to install. You could fix this problem by taking your SD card out when installing an app that won’t install but there are better solutions around.
There are two solutions to solve this problem, one is temporary while the other is semi-perminant. Here are the instructions for the first simple solution that will have to be repeated every time you have the problem:
1. Unmount the SD card by pressing Settings>Storage>Unmount SD card
2. Install the app
3. Either reboot your phone or mount the SD card using the same method as above.
There is a another solution available that requires a bit more work but once it is complete you won’t have unmount the SD card every time you have a problem. I would tell you, you won’t have to deal with the problem ever again if you use the second solution. The truth is though, this is a semi-permenant solution because the folder on the SD card could become corrupt again. Go to the Android Central forums to read the instructions.
Source (Android Central forums)