Try clearing your hard drive cache by doing the following...
To perform the function, access 'memory' in the system blade, and then highlight the hard drive. Now press: Y, X, X, LB, RB, X, X. The following message should appear: "Do you want to perform maintenance on your Xbox 360 storage devices?"
If you initiate maintenance, the hard drive's cache will be cleared, including all software updates.
I am seen problems like this due to bad data loading.