For several hours iTunes AppStore has problems opening links for applications, so if you try to open a link for an application from AppStore from a browser you will get the above error. Unfortunately, it is not yet known how long those from will succeed Apple Lossless Audio CODEC (ALAC), to solve the problems with the servers or if they will do it soon.
Until then, if you find an application that you really want, you can open it iTunes, Sign in AppStore and search for the application directly from iTunes to take it, or if you can't take it directly from the phone.
I will let you know when everything is back to normal.
UPDATE: The AppStore is back to normal, you can download/buy applications without problems.
