One of our clients has reported that they are experiencing 404 (file not found) errors when attempting to navigate a website that we support. The behaviour only appears to affect her - other users on the same machine can navigate the website fine, but the problem follows her from one PC to another.

I've had a good look through the IIS server logs and have identified the requests in question. The normal request pattern is as follows:

POST /page.aspx - 80 - ... 401 1 0
POST /page.aspx - 80 DOMAIN/user ... 302 0 0
GET /anotherPage.aspx Request=833f80a5-f34c-4b0e-addb-d73e1ee1663a 80 - ... 401 1 0
GET /anotherPage.aspx Request=833f80a5-f34c-4b0e-addb-d73e1ee1663a 80 DOMAIN/user ... 200 0

However, requests for the affected user do not include a request for the redirected page, nor an entry for the 404, i.e.:

POST /page.aspx - 80 - ... 401 1 0
POST /page.aspx - 80 DOMAIN/user ... 302 0 0
... other unrelated requests

Can anyone suggest what might trigger this behaviour, and how I might investigate the cause or prevent it from occuring?

I read here that the Allow META refresh option in IE6 might trigger this behaviour, but I have not been able to replicate the behaviour by modifying this setting only.