What causes the "Unable to download application" error on an iPod Touch?

On some wireless networks, whenever I try to download or update an app I get the following message:

Unable to download application.
<Your App> will be available for download when you log in to the
iTunes store on your computer.

I assume it is some kind of firewall issue. Assuming it is, does anyone know what firewall ports are required to download apps via WIFI to an iPod Touch?

Solution 1:

I had this twice on my iPod touch.

When it happened first, there was not enough free memory on the iPod.

The second time it was an app (yxplayer) not designed for the iPod. I even could not install it after I had downloaded it in iTunes. If I remember correctly iTunes told me that this app can not be run on an iPod touch. After i "upgraded" my iPod to an iPhone 4, I could install the app without any problems.

Solution 2:

From the following source:

Have you ever had this error message on your iPhone while trying to download an application or a game: Unable to download application.

There is a pretty easy fix for this and here is how it works:

Simply double tap the icon of the application that gives you trouble and wait for a few seconds. It should then be available.

If it does not work, the problem may also be that the app didn’t get downloaded completely. So, remove it and try downloading it again. I found it much better to download app over wifi, rather than 3G.

Solution 3:

Try Settings > Store (near the bottom) > View Account. I think that if your Apple ID hasn't been recorded, then you will see the prompt to do so, otherwise, you'll just see "View Account" and "Sign Out".

UPDATE: The one other thing I think you should try is make sure your iPhone has the latest iOS it can support. There shouldn't be any need to open/close ports for the App Store on the network; it should just be like any other http traffic. I used to sometimes have the problem you are having, but I haven't in quite a long time and casual observation through other forums shows that you aren't the only who has had this problem, and an upgrade to the latest OS was the fix.

Solution 4:

It happened to me today when my app was approved and available in store. I got same message. The reason it was happening for me because i was using same Apple ID which i used for submitting app. I changed the apple ID and it downloaded without any issues.