What role are you using on that branch ? Does that user have the ability to delete/rename on that branch ? Check the admin tab -> Roles and permissions -> Manage Roles -> Edit the speciifc role you are using -> Files forms and folders look for rename
Guys, Even I am facing similar kinda issue, I have checked the perms in workarea and on file system all are good, just to mention I dint have this issue on the base release tats 672, this is happening when I put SP1 patch over it. Regards,Pawan