I am not Sure as which Operating System are you using on your Computer.
Anyways - If you are using Windows OS. The immediate Fix for this is performing System Restore.
System Restore will put your computer in the Previous State when you were able to upload all multiple photos at once.
In Most of the Cases System restore will Definitely Help.
(the Following Web Link will help you perform System restore)
http://www.sevenforums.com/tutorials/700-system-restore.html (windows 7 or Windows Vista)
http://support.microsoft.com/kb/306084 (Windows XP )
If system Restore Does not work.
Try to Uninstall Silverlight using the Batch File that i have Attached ( It is in a .txt format change it to .bat extension and double click to uninstall Silverlight )
and then Reinstall Silverlight.
If that does not work
Try using a Different Browser . Mozilla firefox / Google Chrome or any other.
If this Does not Work
Then, Please mention the following:
1. The Error Message you get when you try to upload multiple Photo?
2. Any Windows updates that happened prior to the Situation Encountered
Hope this helpzzzzz.
Please reply if need further help.