这是我在查阅PrintingPermission的时候出现的：
Declares that the calling code can access the resource protected by a permission demand through the code that calls this method, even if callers higher in the stack have not been granted permission to access the resource. Using Assert can create security issues.
请各位用自己的理解给小弟解释一下，小弟查了中英文的MSDN，都没看懂, What a shame......
------解决方案--------------------
就是调用当前函数的上层函数（因为函数调用使用堆栈，调用当前函数的函数们叫callers higer in the stack）。