You might want to take a look at the IIS log files to see if you can spot what's different in the requests coming from these workstations from the others. IIS log files are under c:\windows\system32\logfiles\w3svc1 folder

>We have an ASP.NET application being hosted on our IIS 5.0 Server with .NET Framework 1.0 and 1.1. For most workstations, the site hosts perfectly, with no problems. However, some workstations consistently get "HTTP 425" errors. Hitting "refresh" in the browser will eventually get past the error, but users are getting frustrated at this solution.
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>Has anyone else encountered his problem with .NET applications serving fine from some workstations and consistent "HTTP 425" errors on others within the same Intranet?
>
>Thanks
>SLC