Hi,

Even I have not dealt with this AP earlier. but looks like the Lightweight AP can not be converted to Autonomous afer doing a search on cisco.com.

Although there is no document which explicitely states this but this is what release notes states -

Converting an Autonomous AP521 Using the CCA -

When an autonomous AP521 access point is converted to controller-mode operation using the CCA, the access point properties screen continues to indicate that the access point is an AIR-AP521G-A-K9 after the conversion. This is in agreement with the product label on the access point. However, the CCA displays a small triangle icon next to the converted access point to indicate that the access point is now operating as a controller-mode access point.

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Note The CCA conversion process is one-way. Once the conversion takes place, you cannot restore the access point to autonmous operation.

http://www.cisco.com/en/US/docs/wireless/access_point/521/release/notes/iosap521rn1234jx1.html#wp243837

Another link which talks about the conversion of Autonomous to Lightweight with the same restriction. It does not talks about LWAP to Auto conversion -

http://www.cisco.com/en/US/docs/wireless/controller/526/1.5/configuration/guide/A2_aap.html#wp1013636

-> Sushil

I'm no expert with this model. Can the AP join the WLC? If so, I would like to ask if you can invoke the following CLI command on the WLC:

config ap tftp-downgrade

Hope this helps.