Some possible reasons:
The AP3801i is a feature rich,
single radio 802.11ac or 802.11bgn indoor access point (AP)
You are using an E model access point (3825e) which requires an antenna to be selected before the radio will come online
The AP is not talking to it's local controller, it failed over to a backup. It will not take any configuration changes.
Doug Hyde
Director, Technical Support / Extreme Networks