ERROR ITMS-90705: "Launch storyboard not found"

I developped an IOS app using Xamarin Forms. And when i try to upload the ipa file with Application Loader I get this error :
ERROR ITMS-90705: "Launch storyboard not found. Make sure you specify the launch storyboard filename without a filename extension for the key UILaunchStoryboardName in the Info.plist."

I have already this in my Info.plist file:

<key>UILaunchStoryboardName</key>
<string>LaunchScreen</string>

Can someone help me ?