Tar's won't untar ever now in potatoe

[Eric Whitestone <earwax@erols.com>]

	I've been downloading lots of tar files with ncftp and mozilla (which im trying to get rid of by downloading netscape), but when i try to untar /gzip them, it tells me : 
gzip: stdin: not in gzip format
tar: Child returned status 1
tar: Error exit delayed from previous errors

 evyerytime.
	They are the same filesize as on the ones on the ftp servers im getting them from. 

17500414 Jul 25 10:18 communicator-v477-us.x86-unknown-linux2.2.tar.gz
Any quick ideas of what could be causing this..
	thanks

.Eric