>No clear on what you mean by "The update never kicked in". Do you mean that ASP.NET simply did not recognize that the DLL had been replaced or that the replacement *did* trigger the creation of a new domain but that the process did not complete (i.e. the site went down) ?

When that happens, the browser falls in the Waiting... mode. Thus, IIS cannot respond. The new DLL is there. It sits in the Bin directory. But, the site no longer responds. Sometimes, I have to do up to 3 iisreset /restart before the site starts responding again.

Yesterday, once, I succeeded by killing the w3wp.exe process. So, the site starts responding when a new instance of the w3wp.exe process was loaded.

>How long was 'never' ?

It means that if I wouldn't have done a manual step, the site would still not respond.

>I assume the DLL in question is a .NET DLL not COM ?

It is a .NET DLL. For each Web site, I have two DLL in the Bin directory. I have Framework.dll, which is having about 880 KB. The application DLL, for the Universal Thread, is 950 KB. I have another site where the DLL is only 300 MB. This happens there as well. So far, it happens only on my server. There is something on that server which causes this reaction.