Accessing Azure Data Lake Storage from .Net SDK - FsOpenStream error 0x83090aa2

For the topic there is a very good basic example located here:
https://azure.microsoft.com/en-us/documentation/articles/data-lake-store-get-started-net-sdk/
with application authentication and it worked.

But once I tried to connect to the existing data lake store - it won't. Giving me a cryptic error:
Exception of type 'Microsoft.Rest.Azure.CloudException' was thrown
with even more cryptic insides like:
FsOpenStream failed with error 0x83090aa2

I have tried fixing file location, assuming may be /myfile.txt is wrong for the file in the very root. Nope. It is all simple, ...as usual.

Remember giving access to your application to the resource group (or subscription or whatever you choosen)? Well, this is not good enough - you have to give access to the data lake store folder explicitely, as it does not inherit it (as I expected it would).

Browse the data lake store, and click on access - app is not there!

So, giving my app access directly to data lake store root folder solved the error.