Hi Vanessa,
Are you entering any duplicate value(already existing on) during WBS creation->save.
I just searched on this dump and found following SAP notes:
Note 656967 - Application log: SAPSQL_ARRAY_INSERT_DUPREC, BALDAT
Note 196113 - SAPSQL_ARRAY_INSERT_DUPREC, BALHDR
Please check these notes. You can also discuss with ABAPer on ST22 dump analysis.
Thanks