In 'Special Notes for Upgrades' in the Datacom installation guide when upgrading from Datacom r11 to r12 , it is mentioned that the CXX version needs to be version 11.0 before starting the upgrade process.
How to check this version?
Have a look at message DB00905I - DIRECTORY (CXX) VERSION nnnn
which is given during the Datacom Multi-User (MUF) startup like in following example:
DLV1M110:DB00905I - DIRECTORY (CXX) VERSION 11.0
If message DB00905I says its version 10.0 then convert the CXX to version 11.0 first by following the instructions in the Datacom installation guide.