i hv error in servlet (java),plz anyone help me?

C:\Users\HP>d:

D:\> cd D:\app\WEB-INF\classes

D:\app\WEB-INF\classes>javac MyServer.java
MyServer.java:4: cannot access javax.servlet.Servlet
bad class file: D:\Tomcat 6.0\lib\servlet-api.jar(javax/servlet/Servlet.class)
class file has wrong version 49.0, should be 47.0
Please remove or make sure it appears in the correct subdirectory of the classpa
th.
public class MyServer implements Servlet
^
1 error
this error cme whem am open tomcat server,and also not compile java file,above error is cme,any body tell me about this.?