Follow Jaroslav's suggestion.   The workaround was to physically power off the switch for 5 minutes, then power it back on. A remote reboot does not help, it has to be physical. After power on, the message disapeared and the switch works well.

Jaroslav is right even after 2 years. Here is what I experienced.   1- Stack of 4 WS-C2960X-48FPS-L 2- Old IOS was c2960x-universalk9-mz.150-2.EX5.bin 3- New IOS that gave the ILET error - c2960x-universalk9-mz.152-2.E7.bin. Then we reloaded the stac...