When I or any other user on any machine tries to change the navigation through Site Actions - Modify Navigation, an error occurs stating
"The security validation for this page is invalid. Click Back in your web browser, refresh the page, and try your operation again."
This error occurs throughout the farm and has only been noticed since we applied the June CUs last week. I don't think this error occured prior to this, though can't be sure as chagning the navigation doesn't occur frequently.
I have however, been able to make an urgent change using the object model through Powershell directly on the MOSS server.
The ULS has an entry below
Area: Windows SharePoint Services
Level: High Message: (Error as recorded above)
I can't find any recurring messages surrounding this entry.