Problems Posting (Certain ISP)

[Ghostsuit]

Ok I've upgraded our board to 2.2.4 and now a certain ISP's broadband service (NTL) are having problems posting on our site. I asked one of my users to try posting at vbulletin.org and they get the same problem but they can still post on a vBulletin board running 2.2.1 any idea what the problem is?

Now the dial up service works fine for the same ISP. I'm at a total loss since alot of my users use this service.

[Ghostsuit]

Sorted while the ISP was telling customers it wasn't them I finally got throught to the ISP and after a lengthy discusion it would seem that it was them.