During an upgrade with target Release 4.5B FCS (First Customer Shipment), error message
1AETW000 ===> PANIC: creation of shadow class XXX failed with rc 0
is displayed in one of the phases DIFFEXP* (DIFFEXPMOD, DIFFEXPCUST, DIFFEXPGEN,...). Additional key words
'XXX' is the name of any class.
The export then ends with exit code 16.
R3trans, return code 16 Cause and prerequisites
The cause is a program error. Solution
https://service.sap.com/sap/support/notes/146773 (SAP Service marketplace login required)