I got the error “ORA-21561: OID generation failed” when I tried to connect in rman catalog. To solve this problem, you need to edit the /etc/hosts file and add the name of the machine (host).
The text above I wrote in 2015 while I was using the database version 11g. Now in March 2020 I faced the same error and despite of the fact that the version in this new case be 12c and I was trying to clone a virtual marchine from another the solution was the same : modification of the hosts file. It is kinda funny you google the error and find the solution in your own blog :).
