Product and Software: This article applies to all Aruba controllers and ArubaOS versions.
The inactive (I) flag indicates that the AP has no virtual APs active and, if the AP has wired AP ports only, those are not active either. The I flag could also be due to radios being disabled under the radio-profiles, the ap-group not having any VAPs, and the VLAN of VAPs being undefined on the controller.
If GRE is blocked, that should cause the AP to continually bootstrap. It will appear to be active for the 8 seconds (by default) it takes for the AP to decide that the tunnel is not there. The AP will show as inactive briefly between the times the AP reboots and the time the controller configures the virtual APs.
The U flag is displayed any time there is an unknown group, unknown name, and gain not provisioned, because the AP considers these all as "unprovisioned". Because no virtual APs are created on an unprovisioned AP, it is also considered inactive.