Make the contents of the entitlements plist file...
(from http://stackoverflow.com/questions/5449487/iphone-entitlements-problem-with-xcode-4-for-ad-hoc-distribution)
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<!--- Required entitlements (in most cases shouldn't be changed) --->
<key>application-identifier</key>
<string>$(AppIdentifierPrefix)$(CFBundleIdentifier)</string>
<key>keychain-access-groups</key>
<array>
<string>$(AppIdentifierPrefix)$(CFBundleIdentifier)</string>
</array>
<!--- Custom entitlements below --->
</dict>
</plist>
via code signing – iPhone Entitlements problem with XCode 4 for Ad Hoc distribution – Stack Overflow.