I have a classic asp ajax chat application that has been running just fine for years on windows server 2003. But I just recently upgraded the server and now on server 2-008 r2 with iis 7.5 and the ajax refresh takes 3 times as long as it should. I have tested the same code again in the same browsers on iis 6 and there are no problems. With it running on iis 7.5 when it should be refreshing every 3 seconds, it is actually only refreshing about every 9-15 seconds.
I have also noticed that the issue is not a bad with firefox, chrome and safari as it is on IE.