Some of the Grade Center problems have been resolved, including the issues related to submitting test attempt, clearing test attempt, and the duplicate assignment download and clear links.
The remaining Grade Center issue is related to navigating to a locked test attempt. The link below will explain the problem and provide a work-around. However, at this time, new YouTube mashups are not working (existing ones are fine) and there is a menu problem for unavailable courses.
The following document will provide more information and workarounds:
NOTE About CALENDARS: There are some issues with the Calendar display and due dates displayed in the My Calendar module. More information will be posted at a later date. The Calendar display can be resolved by using Firefox or IE 8 browser (but not in compatibility mode).