This can occur if the BPPM cell’s KB was not migrated properly. In 9.0, relationship class definitions are in mc_tm_root.baroc and mc_tm_relationships.baroc. If those are not loaded, that will cause this problem.

After correcting the KB to load those files, you will need to restart both the cell and jserver as the cache will not be corrected until the jserver process is restarted.