What is the common aspect of the failure? From your description, it seems to be one specific ISP.
If so, then they are the problem, no matter what they say.
Hmm true even I thought its ISP but the same ISP provides mobility service and on their 3G network the site works.. Seems its the ADSL Broadband which could be an issue? But most striking is that it started after i upgraded to W7 ultimate