Images and files are stored is the NVRAM. Even if files are deleted from this memory, some files remain and can be un-deleted later. To completely remove these files, squeeze them. The error message occurs when you try to upload or downgrade the firmware.
To format the Flash and reload the Cisco IOS firmware image, perform these steps:
Download the image of the firmware you are using from Cisco.com and copy it to the computer where on which the TFTP server is installed.
Copy the current configuration of your Access Point (AP) on your computer. Go to System software > System configuration > Config.txt, and copy it on you computer.
Make a console connection on your AP.
Issue the appropriate command in enable mode: AP-Hostname#format flash: mode.
Note: Do not close the hyperterm window when it is formatting Flash. Once it is closed, the AP boots in AP mode.
Once it formats the Flash completely, you can re-load the image by issuing this command:
Archive download-sw /overwrite /force-reload tftp://ip address of PC
running TFTP service /Name of the image of 12.3(7)JA with extension tar
Copy the configuration file that was saved on the computer back on the AP.