I've seen similar postings, but not quite the same. I have a newly installed Windows XP Pro system with SP1a and all the updates from Windows Update. I have IIS 5.1, which I have completely removed and re-installed to try to solve this problem, but same problem. Any page, including html, results in Server Application Error, and the event log has:
The server failed to load application '/LM/W3SVC/1/ROOT'. The error was 'Class not registered
'.
File permissions are open to Everyone, just as an attempt to solve this problem.