When I try to open any ASP page from the Altiris Console, after the "friendly HTTP errors" (in Internet Explorer under Tools > Internet Options > Advanced > Show Friendly HTTP error messages) option is turned off, I see "The request resource is in use."
As well, when checking the IIS logs, any request to postevent.asp page is getting the HTTP Error 500 as well.
If the above suggestion didn't work:
Another suggestion could be to make sure that all the updates available for Windows, IIS and ASP are installed.
Notification Server 6.0.6074 SP3 R8
SQL Server 2000
Windows Server 2003