Hi,
This may be a case when you are using two App42_Unity_SDK in your application.Actually our sample Unity Package also conatins the App42_Unity_SDK as well. You can remove one of them.
If you want to integrate in your application than import UnityPackage that is available in sample project. You need not to add additional SDK and you can easily use Storage Service.
Let me know if it helps.
Thanks
Vishnu Garg