Problem logging in with IE9

The client has reported that one customer only is complaining about having difficulty logging into the site using IE9. The site has been live for 4 weeks now and apparently the customer could login ok with IE9 for the first two weeks but for the last two weeks cannot login. We have not changed anything on the site and for everybody else the site is working perfectly and to date there have been 2346 visits to the site with 690 visitors using IE9. We use IE9 and have never had a problem logging in.

We have explained that these statistics suggest there is not a problem with logging into the site with any browser and it is probaly due the configuration of IE9 on the customer's computer. However the client wants to resolve this issue with this customer.

These are the questions we asked the client to send to the customer and their answers are shown alongside.

1. What exactly happens specifically? Answer: Open up the homepage, click log in & nothing happens just stays on the homepage.
2. How often does it happen, always or just sometimes? Answer: Every single time.
3. Do they have cookies disabled on their browser? Cookies are needed to make the site run properly as we say in the T&C. Cookies are specific to each browser. Answer: Yes we have cookies on the computer.
4. Can they login using another browser on the same computer? Answer: Yes currently using safari which works fine.
5. Have they tried another computer? Answer: Yes all other computers work.
6. Is their version of IE9 up to date with all the latest updates? Answer: Yes all updated.

Based on this information can you suggest a reason for the problem and a possible solution.