Sharing a web server between development teams is always fun (not).  We had a problem surface today (or resurface) where if a developer creates a web application on IIS that uses .Net 1.1 for example (not an uncommon occurance) and some other developer creates a web application on that same server but this second one uses .Net 2.0 (something becoming more common every day).  Odds are that the developers and even sometimes the network engineer or web master will allow the defaults to lull them into the false sense that it was an easy and straightforward task.

The problem is that they both allowed the "Default Application Pool" to remain selected and now the second of these sites to load will crash IIS.

You can't have two different versions of .Net loaded into the same process and Application Pool often (though not always) means the same process.

Scott Forsyth has an article about this very issue that will help describe the error that occurs when you have this problem (the "Server Application Unavailable" error).

If you haven't seen this yet, then you will.