IDoc from ECC --> PI 7.31: Rollback fault: Not defined type....

hi guys,

When sending an IDoc from ECC to PI 7.31 via IDoc AAE adapter, the IDoc remains in SM58 in the backend with the following error:

Rollback fault: Not defined type of Handler class com.sun.proxy.$Proxy462

In PI's default trace a similar error shows:

JCO_ERROR_SYSTEM_FAILURE: Rollback fault: Not defined type of Handler class com.sun.proxy.$Proxy462

Any ideas ?