[Q] Secure Fail: Kernel after downloading Clockworkmod recovery with ROM manager topic

I have Samsung Galaxy S III Verizon.
Rooted with Kingo ROOT.
I was trying to install a custom ROM so I had to download ROM Manager to install Clockworkmod Recovery.
After doing so, however, whenever I try to go into recovery mode, a screen with SECURE FAIL: KERNAL, a yellow triangle with an exclamation mark, and the message "System software not authorized by Verizon Wireless has been found on your phone. Please turn off your phone and go to the nearest Verizon Wireless store for help" comes up.
Then the the only way to access the device is to go to download mode and then cancel it because if I try to turn the device on the normal way, it keeps on going to recovery mode and the fail message.
I tried manually installing CWM using a computer, but when I type in "fastboot devices", nothing shows up. I tried everything including pdanet and other stuff but none work.
I can't even factory reset or anything.
Don't know what to do.
I just want to install a custom ROM.
Please help. I have been stuck on this problem for days.