Problem accessing certain URL's, others okay

Hi all, a bit of an oddity here. We have a customer using Windows 2003 Server SBS, Windows XP workstaions   ( All SP2) and they are having problems accessing some web sites. This all came about, coincidentally, after upgrading to the latest Symantec Antivirus/Antispam. So now there are certain sites which cannot be accessed, the browser just times out. One example is www.lme.co.uk we cannot open that site at all, but we could. Another is www.experts-exchange.com !!! there are probably lots more that we cannot access, but at the same time there are lots of site that are no problem. We have the standard configuration of two network adaptors, one for LAN and one connected to the Firewall. The configuration of the firewall and router have not changed, neither has the configuration of the IIS. Any clues anyone, oh yes if we try to 'tracert' to www.lme.co.uk we get a trace, but if we try to 'tracert' to lme.co.uk get the messsage "unable to resolve the target system name lme.co.uk" ??
Thanks in advance
Jonathan_HellerAsked:
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CetusMODConnect With a Mentor Commented:
PAQed with points refunded (125)

CetusMOD
Community Support Moderator
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pseudocyberCommented:
I've seen problems browsing - where random sites won't work and some will, and pings working fine - related to MTU.  If you lower the MTU on the Internet connection - firewall, router, whatever, then it works.  However, this wouldn't explain why it was working and now it isn't.

What if you roll back the symantec antivirus/antispam upgrade?
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Jonathan_HellerAuthor Commented:
Please could someone tell me how to cancel this question as it turned out that the hardware firewall had become unstable and required replacing.
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