Error “An unhandled exception occurred in the Silverlight Application” when creating a new site via Silverlight interface

If you get the above error when creating a new site via the Silverlight interface, here’s what should fix the error:

Go to Central Admin, klick “Manage Web Applications”, choose “General Settings” and check if Security Validation is turned off. Turn it on!

securityValidation

You will now be able to create sites using the Silverlight interface again.