Git无法删除本地分支：不允许操作

Question

尝试删除本地分支时出现以下错误

>>> userx@userx-VirtualBox:/media/workspace/project$ git branch -d issue56
error: error replacing .git/packed-refs: Operation not permitted
error: Error deleting branch 'issue56'

.git /目录权限drwxrwx--- 1 roort vboxsf