Jira Server App integration -> java.lang.NoClassDefFoundError

Hi there,
I’m getting a java.lang.NoClassDefFoundError when my app is trying to use a class imported from another app. If my app is installed after the other which integrates, all it’s fine. If the other app is installed after my app, I get a java.lang.NoClassDefFoundError.
Is there any way to reload the class loader or the plugin OSGI container?
Any suggestion?