ORA-00935

select owner,sum(bytes) sumb 
  from dba_segments 
 group by OWNER
 order by sum(bytes) desc
;

ORA-00935: group function is nested too deeply

Oracle Support Document 18529.1

Error:  ORA 935  
Text:   group function is nested too deeply 
-------------------------------------------------------------------------------
Cause:  This is an internal error message not usually issued.
Action: Contact customer support.

The fix for my query is not to use the aggregate in order by:

select owner,sum(bytes) sumb
  from dba_segments 
 group by owner
 order by sumb 
;