Consumer failed to build

Jun 1, 2016 at 7:32 AM
I have downloaded all the libraries, and included them in the LtiSamples project.

All errors are solved except for this: LtiRequest gives error:
The type 'ILtiRequest' is defined in an assembly that is not referenced. You must add a reference to assembly 'LtiLibrary.Core, Version=1.5.5467.17178, Culture=neutral, PublicKeyToken=null'.

When I'm trying to add the Referenced Library to the project, it says it already exists.

Not sure what to do.