Please post the error. If the error occurs during the boot and the WLC fails to fully boot up and you don't get a prompt, then most likely your image is corrupt or your unit just failed. Either way, you will need to open a TAC case to either get a recovery image and the direction to upload that to the WLC or else you will have to RMA the unit. You would need a support contract to open a TAC case though.
If your WLC does boot up okay and you get a prompt, then your in a better spot:). Just post the error.
Transferring Crash file from standby: Login to the Active WLC in HA.
From CLI: (Cisco Controller) >transfer upload datatype crash (Cisco
Controller) >transfer upload filename (Cisco
Controller) >transfer upload mode tftp (Cisco Controller) >transfer
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