enanthate:
Can't use Internet Explorer!
...
Any thoughts on why this happens?
Just tested IE 9 and it works fine ( for IE anyway ), what version is yours?
An old cache file may be causing the error, you can stop IE from caching old files while Arduino.cc is being updated.
click the menu item 'Tools > Internet Options'
Under the section 'Browsing history' click settings.
Where the dialog says 'Check for newer versions of stored pages:' select the option 'Every time a visit the website.'