What version of IOS are you running? According to the release notes for IOS XE Software-3.6.0E(ED) the 3850 now supports the 2700 series AP.
Release notes found here: http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3850/software/release/3e/release_notes/OL3262101.html#pgfId-919177
Ryan is right, IOS-XE 3.6 added following AP support
Support is added to the following APs in this release:
Note The Cisco Aironet 1530 Series APs are supported operating only in Local mode; these APs in mesh mode are not supported.
If you are running this version of software & still cannot register your AP, then attache the AP console output to see what's the reason for failure.
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