What did you already try.
1 Delete tempory files and IE history?
2 Change default down load to internal memory.
3 Soft reset after above.
4 try to push it to your phone via www.windowsphone.com
5 is it the only app where you have problems with.
6 Is it downloading or updating the ap.
7 If its updating did you try to uninstall it and than downloading it again. (via store and window phone.com?