Google app engine and Google checkout notifications error

I'm just having problems getting the custom order processing tutorial to work.

Has anyone had luck with this?

I g开发者_如何学运维et the following errors:

Error for /myapp
java.lang.NoClassDefFoundError: com/google/checkout/sdk/commands/EnvironmentInterface
    at java.lang.Class.getDeclaredConstructors0(Native Method)
    at java.lang.Class.privateGetDeclaredConstructors(Class.java:2406)
    at java.lang.Class.getConstructor0(Class.java:2716)
    at java.lang.Class.newInstance0(Class.java:343)
    at java.lang.Class.newInstance(Class.java:325)
    ......

Any suggestions?

Just trying to receive notifications of new purchases at this point.

Make sure the jar that contains EnvironmentInterface is in WEB-INF/lib, as well as on your classpath.