What is the complete description / name of the license you are attempting to install?
Prior to AOS 5.x we did have separate Remote AP (RAP) licenses and Campus AP (CAP) licenses. We did away with the RAP license and now the AP license (LIC-x-AP) takes care of both AP types.
Now, if you started with this controller on AOS 3.x and had installed both the RAP and CAP licenses then upgraded the SW to 6.x the RAP licenses would have been converted, automatically, to regular AP licenses.
You can go into the License Management System and view the pre-5.0 versions of your licenses and the post-5.0 versions at : https://licensing.arubanetworks.com/