I have the same experience. Tried to download/install the 1.2 Gb Instrument pack three times in March. Deleted the entire Garage Band the other day, then downloaded it again and Installed OK. But the same message showed when I tried once more to download and install the Instrument pack: Failure! What is wrong?
Mac Mini purchased december 2011, OS 10.7.3 LION
So I'm experiencing this problem as well. I've tried downloading this from my home internet as well as a hotspot and still no luck. The connection with the server times out and the download ceases. When the full download was able to take place, I got the error "can not verify package".
I'm using a macbook air 2 with 10.7.4 and mountain lion
Thanks for any help!