I have encountered a really strange problem that, despite trawling teh internets and the dev forums, I can't seem to solve. It is also very confusing, and seemingly has no pattern to it.

I have setup a Visualforce page that renders to PDF, and can be opened and printed from the Opportunity page.

However, one user seems to be unable to open the page from Internet Explorer 8 on her machine. When she tries to open the page, a window opens with the correct url, but before it loads the page, it cancels itself.

Her profile and role are the same as mine (admin), yet when I log on to SF on her machine, I can open the page in IE without any problem. To add to this, if she logs on in Firefox on her machine, or in Chrome on a Windows 7 machine, she can access the page ok.

Stranger still, if she logs on to IE9 on the W7 machine, she cannot access the page - it just repetedly rediects her back to the SF login screen. But if I log on to the same browser/machine, after one extra login, I can access the document.

Note that, whilst we have the same profile and role, I have the admin functions ticked in my user profile, whilst she does not.

Also note that I have tried 

cache="true"

and

standardStylesheets="false"

in the page descriptions, but neither solve the problem.

Can we find a solution, or is a browser change the only option?

Thanks in advance.