Transfer Tasks failing with ORA-28040 after Upgrading AWR Warehouse to 12cR2

Checking the AWR warehouse health after we upgraded the repository database from 12cR1 to 12cR2 I noticed that for some source databases the transfer task had been failing.
Performing “Upload Snapshots Now” I was also able to reproduce the problem and identify the error message “ORA-28040: No matching authentication protocol”.

This was initially puzzling as the source database was version 11gR2, and in 12cR2 the default value of the parameter SQLNET.ALLOWED_LOGON_VERSION_SERVER is 12, which should allow connections from 11gR2 databases.

A bit of troubleshooting identified that the transfer task uses the Instant Client bundled with the OEM agent for this task.  The agent version was 12cR4, (we can’t use a later version of the agent as this is running on RHEL5) and the Instant Client bundled with it was 11GR1.

I updated SQLNET.ALLOWED_LOGON_VERSION_SERVER in sqlnet.ora of the AWRW repository database, and the AWR transfer task completes without issue.