Bug 5893340 : ORA-600  [hash aggregation can't be done] can occur
for a GROUP BY query if hash aggregation is chosen.
Fixed on 10.2.0.4 and up.
Bug 6471770 :
Group-By queries can fail with ora-32690 or
ORA-600  [hash aggregation can't be done]
when operating on a large volume of data if hash group by
aggregation is used.
Also, it is possible for hash group-bys to over allocate memory beyond
the limit impose by the auto-memory manager.
Fixed in 10.2.0.5 and up
In order to avoid the erros from both bugs :
1) Disable Hash group-by by setting
"_gby_hash_aggregation_enabled" to FALSE,
2) Use NO_USE_HASH_AGGREGATION hint on your query