Odd isn’t it… We used to use an ajax call on that and it caused so many problems that we moved to a 100% standard HTML file upload control and have had – no ends of problems!
Do you now how to use the script console by any chance? If so can you have that open and then try the browse button to see if any errors are reported. Failing that would you be able to create us an account so we can get to the profile to take a look? if yes to this let us know and I will tell you what we need.
In the meantime – what is the plugin called ‘jquery-updater’ for and what does it do please? I suspect it is loading an incorrect copy of the jQuery library…