403 when trying to save an UIdesigner Form

Hi,

Pretty much everything is in the title. I can't save any form from UIDesigner, even if I haven't made any change to it :

The javascript console reports an HTTP 403.

I have tried to restart the web server and to reset the engine, without success. There's nothing in the logs (I checked both bonita.log and catalina.log).

I'd like to avoid uninstalling and reinstalling the studio