Downgrading 5200 wireless controller from delivered code 10.11.03.004 to site code 09.21.11.0004

[Rod_Robertson2]

My cleints have attempted to down grade a 5200 unit to verion 09.21.11.004 from the supplied version of 10.11.03.0004 ( this is so it matches the current operational box )

The downgrade has failed with the following prompt:
Error! Upgrade is not supported from major release :10

I would like to know how can I can downgrade the unit to the required software level

[Rod_Robertson2]

Sorry I cannot access the https link , do you have another as this keeps directing me to my internal 365 account.

[Ronald_Dvorak]

Downgrade isn't supported instead you load a rescue image with another/older firmware.

If you don't have a 9.21 resuce image from another C5210 you should contact the GTAC.