Most likely because the 1st time you received a corrupt error message, you ticked to always use this answer. So it means your downlds that detect any corruption will automatically be set to corrupt. To undo this, go to the LW menu Tools>Options>View>Popups & tick Revert to Default option & press the apply button.
At least with the option, LW may attempt to re-downld the corrupt part of the file. I guess it depends on how it was detected as being corrupt.
See Corrupt files due to firewall:
http://www.gnutellaforums.com/showth...threadid=39368 as this 'might' apply to you.