You probably didn't put it into pwned DFU mode. Use the redsn0w version that it included with whited00r and go to extras, pwned dfu mode and follow the instructions.
I had the same problem too using the incorrect version of redsn0w.
Overcome the issue, try using the redsn0w that came with the whited00r download from the official whited00r website (should be in the zip file containing the .ipsw file).