ora-12801 and ora-01722 when using PARALLEL hint

[samdba]

Hi all,

I am getting foll. error when using PARALLEL hint and works fine without the hint.

ora-12801: error signaled in parallel query server P005
ora-01722: invalid number

This error comes on the foll. line in SQL statement.

AND papfa.person_id = DECODE(haaif.attribute3,NULL,papfss.person_id,TO_NUMBER(haaif.attribute3))

What could be the reason?

Thanks in Adv.