When utilising Internet Explorer, the Sign In button may cease to operate or not allow the user to enter their credentials. A browser error may be thrown, indicating a script conflict.
This is a known issue caused by the DivX Web Player plug-in, and only affects users who have downloaded and installed this plug-in to their browser.
The immediate solution is to disable the DivX Web Player plug-in:
Open Internet Explorer, then click on the "Tools" menu, then select "Manage Add-Ons".
In the resulting pop-up window, scan for the DivX Web Player plug-in in the listing.
Once located, select the plug-in, then click the "Disable" option along the bottom.
Close the window and refresh the Ultranet page, after which the Sign In button should operate as normal again.