Can't see namespace of External library (portable)

Hello,

I trying ASP5 in VS2015 and run into a problem.

I have created an external library (portable) Called "TestLib" that is targeting .net Framework 4.6 and ASP.net core 1.0

On one MVC5 application after reference the project "TestLib" any class can  see it so no problem in "using TestLib".

on ASPC5 I can also reference the "TestLib", but cannot use the reference "TestLib", it's namespace is not visible.
so I CANNOT add "using TestLib" on Header or call any methods on that lib.

I can see that after adding reference it appeared on project.json but Cant't use on any .cs file:

"frameworks":{"dnxcore50":{"dependencies":{"TestLib":"1.0.0-*"}}},

What can I be doing wrong or missing? thank you.