Issue with @PreAutorize annotation with Spring Security

@PreAuthorize is not working in Spring Security 3.

This is my code snap.

 @PreAuthorize("hasRole('Admin') or hasRole('Student')")
 public void doSomething(){}

It is giving me weird error (refer attachment)

for other interested people..

I fixed issue by adding

<aop:config proxy-target-class="true"></aop:config> 

line in spring-security.xml