No FTP Put from Windows through squid

I ahve just installed squid 2.5 for proxy replacing an old NT box. Works great except FTP from any client computer. All clients are running either win XP or 98. They continually get an error of Read only when accessing FTP site. Looking at the log, not PUT requests are ever shown on the squid box. We can however FTP happily from the squid box directly or from any machine going through the old NT box. Configured client are 192.168.2.1 with a port of 3128 for everything. Thanks for any help, David