Silverlight applications can put information into the computer’s clipboard. But only when the user grants the application access to it.
So while using Silverlight apps online you might have come across this dialog:
I accidentally clicked “no” once and had lots of trouble to reverse this step because I haven’t been prompted this question again.
Even google was no help in this case. Neither was re-installing Silverlight.
Finally a heroic search in the registry gave a solution. There is a place in the registry where Silverlight places the information about clipboard access.
Inside that Key is a subfolder for each Silverlight application that has prompted this question. If you delete the proper folder, you will be prompted again the next time.