Well had another problem all of a sudden with SP 2010.
I wasn’t able to make any list or library because this error kept popping up.
So again thinking of what did I do now, what did I changed that wasn’t allowed to? For a change I didn’t do anything that wasn’t allowed , deployed a few webparts, but that couldn’t be the problem.
After some searching I can across this site ( link)
It stated that it could be a production bug.
If you go to the central admin -> manage web apps -> general settings of the web app with the problem and re enable the security validation. Wait a minute, yeah i’ve changed this not to lang ago because I had issues with some generating/adding open xml (office) documents.
No that can’t be it….. Sure enough the error was gone.
The short explenation: Silverlight Application is unable to connect to the WCF endpoint configured by the product for enabling Client Object Model, if Security validation is set to Off. (copy/paste from the site)
hope this will help someone in the end. It’s a stupid error to have, but an error none the less 🙂