Trying to install an enterprise app on an iPhone and iPad from my web server. The iPhone worked fine but the iPad was failing with the above error message. Me and Justas racked our brains and lost many sleepless minutes trying to figure out what was wrong.
After losing all hope, I tracked down the problem to a simple casing issue. Specifically, the icon image for the iPad, which had a capital letter in the name on the server but I typed the name in lowercase in the plist file. So, actually the ipa, the plist could be downloaded fine, but the download failed for the icon.
Correcting the case of the icon fixed the problem and the app is downloading now. So, be very careful with your paths and if you have this error, check you can download all the resources from a web browser from your server, the icons, the ipa, the plist files.