ORA-08005: specified row does not exist / ORA-08103: object no longer exists?!?

I lately came suddenly across mentioned Oracle errors after bringing a newly develop workflow to integration and acceptance test. We first had deadlocks and removed parallel runs of sessions eventually getting mentioned errors. I noticed after a good deal of search that the connections have not been adapted to the new environment. After having fixed the connections, all runs smooth again. We did not (yet) re-parallelise however.