some ftp sites not opan in squid transparent proxy
 

i am using centos5 squid ver 2.6.stable6, transparent proxy server
in my proxy ftp://ftp.symantec.com/public/updates/ is open but
ftp://aphysics.lanl.gov/pub/collins/latex this ftp site is not open.

if i am using another isp connection both sites are open.

what is the problem?
kindly resolev my question

active and passive mode?
Don't know if this can be set in squid though