ORA-06510: PL/SQL: unhandled user-defined exception
ORA-06512: at "CTXSYS.CTX_DOC", line 1478


looks like CTXSYS.CTX_DOC has raised a user defined exception which in not being handled by the code.

Long term solution is to check the code and fix it.
Exception may be caused by bad data, if that's the case fixing the data would be a nice workaround.