This problem took me a few days to sort out.  We just started using Ajax in our application and everything was running fine, loading fast and being totally awesome (because its Ajax , and I heart Ajax).  I couldn’t figure it out, every browser and every O/S this was working fine, there was just one customer using IE6 with windows 2000.  The problem was the Ajax call was hanging, for a really long time.  At first I thought the Ajax wasn’t firing at all, but with out live http headers for IE6, there wasn’t any way I could confirm this.

So after about 5 minutes of sitting there pulling my hair out…..the ajax returned a result and the next part of the process ran.   Sooo….what the hell?!?!  A few days of googling, trying different things, asking other people in the development team, and finally praying (all religions), I came across a blog post that explained that IE6 doesn’t handle closed connections very well.  We had this line in our javascript:

xh.setRequestHeader(“Connection”, “close”);

We now had to change our code to only include this if the browser was not IE6.  I wasn’t sure what performance hit this would have or what side affects it would have, but we’ve been running this for a few years and haven’t seen any difference with performance or had any problems.  If anyone else has a better understanding of why IE6 behaves like this, please leave me a comment!!