Try rebuilding the App in Apps portal, re-download and sign it. This should fix the issue. Also try re-installing Application Loader.
However if you still encounter same error then contact Adobe Experience Manage Mobile (previously DPS 2015). You can locate contact information at bottom middle after logging into https://aemmobile.com.
Along with unsigned and signed IPA (can use file sharing site like Dropbox or WeTransfer), and Application Loader version.