AP 2802 can not join WLC 5520

[Leo6]

I have Cisco AP 2802E can not join to WLC 5520, log detail:

[*04/05/2023 10:32:27.0005] CAPWAP State: DTLS Setup
[*04/05/2023 10:32:27.0385] dtls_verify_server_cert: Controller certificate verification successful
[*04/05/2023 10:32:27.6947]
[*04/05/2023 10:32:27.6947] CAPWAP State: Join
[*04/05/2023 10:32:27.6986] Sending Join request to (ip address) through port 5264
[*04/05/2023 10:33:24.0339]
[*04/05/2023 10:33:24.0339] CAPWAP State: DTLS Teardown
[*04/05/2023 10:33:24.1144] status 'upgrade.sh: Script called with args:[CANCEL]'
[*04/05/2023 10:33:24.1756] do CANCEL, part1 is active part
[*04/05/2023 10:33:24.1901] status 'upgrade.sh: Cleanup tmp files ...'
[*04/05/2023 10:33:24.2261] Dropping dtls packet since session is not established. Peer (ip address)-5246, Local (ip address)-5264, conn (nil)
[*04/05/2023 10:33:24.2263] Discarding msg CAPWAP_WTP_EVENT_REQUEST(type 9) in CAPWAP state: DTLS Teardown(4).
[*04/05/2023 10:33:24.2263] Discarding msg CAPWAP_WTP_EVENT_REQUEST(type 9) in CAPWAP state: DTLS Teardown(4).

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AP Image Version: 17.6.4.56

WLC Version: 8.10.151.0

[marce1000]

 - The AP may have left over configuration(s) from previous use , checkout this procedure and try it out:
                      https://mrncciew.com/2013/03/17/ap-registration/

 M.

[Rich R]

More likely incompatible software versions.  17.6 code had changes to CAPWAP protocol which 8.10.151.0 will not understand.
You should upgrade your WLC to a fully supported recent version of code - see TAC recommended below.
Current latest is 8.10.185.0.
Otherwise you may need to manually install the 8.10.151.0 AP code on your AP before it can join the WLC.  I suggest you upgrade the WLC rather because otherwise you'll have this problem with new AP hardware revisions (not supported on old code at all) and any with new software installed.  See links below.