untar problem

Hi,

I've downloaded the validator tar ball a couple of times on different days and everytime I try to extract it I get the following error...

x ./validator/htdocs/sgml-lib/pro/usr/local/lib/sgml/iso_8879-1986/entities/genera
l_technical, 4371 bytes, 9 tape blocks
tar: directory checksum error

I'm using the command gunzip -c <filename> | tar -xvf -
Any ideas why I keep getting this?  I've never received this sort of error before and I download and do this fairly regularly...

thanks

 - Steve