This problem seems to be specific to IE9. (IE9 on Win7 32, 4Gb RAM with an NVidia GeForce 8600GTS vid card.)
The Twitter home page seems to be downloaded, the favico appears in the tab, the Verisign Certificate is accessible but the screen is blank white with nothing displayed.
If Google is used to find Twitter, the link seems to work as described in the previous sentence, but the screen remains displaying the Google search results, with all the links inactive (after clicking on the Twitter link).
This failure to display is why I identified my vid card, though it's fine otherwise and has, AFAIK, the latest correct driver.
There are no other apparent issues with IE9, and other sites, secure or otherwise, download and open just fine.
Twitter works fine in FF12 and Chrome.
Searching with Google suggests this problem is not unknown, but none of the solutions offered work.
Load up IE with no add-ons
Reset IE settings
Check latest version of Flash was installed
Repair IE (from http://iefaq.info/ )
Eventually I rolled back to IE8, and while the fonts look a bit pixellated, Twitter can be accessed as expected.
Funnily enough, this does not happen with IE9 on my Win7 64 bit Sony laptop.
Any suggestions as to where to look next?
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